Tubular titanium oxide particles and process for preparing same

ABSTRACT

The process for preparing tubular titanium oxide particles comprises subjecting a water dispersion sol, which is obtained by dispersing (i) titanium oxide particles and/or (ii) titanium oxide type composite oxide particles comprising titanium oxide and an oxide other than titanium oxide in water, said particles having an average particle diameter of 2 to 100 nm, to hydrothermal treatment in the presence of an alkali metal hydroxide. After the hydrothermal treatment, reduction treatment (including nitriding treatment) may be carried out. The tubular titanium oxide particles obtained in this process are useful as catalysts, catalyst carriers, adsorbents, photocatalysts, decorative materials, optical materials and photoelectric conversion materials. Especially when the particles are used for semiconductor films for photovoltaic cells or photocatalysts, prominently excellent effects are exhibited.

TECHNICAL FIELD

The present invention relates to tubular titanium oxide particles usefulfor applications to catalysts, catalyst carriers, photocatalysts,photoelectric conversion materials, decorative materials and opticalmaterials, and a process for preparing the particles. The presentinvention also relates to photovoltaic cells and photocatalysts usingthe tubular titanium oxide particles.

BACKGROUND ART

Titanium oxide particles and titanium oxide type composite oxideparticles are applied to various uses taking advantage of their chemicalproperties.

For example, these particles are used for oxidation-reduction catalystsor carriers, decorative materials or plastic surface coating agentsutilizing ultraviolet screening power, anti-reflection coating materialsutilizing high refractive index, antistatic materials utilizingelectrical conductivity, functional hard coating materials utilizing acombination of these effects, and antibacterial agents, antifoulingagents or super hydrophilic coating films utilizing photocatalyticactions. In recent years, further, titanium oxide has been favorablyused for photocatlaysts or so-called photoelectric conversion materialsfor converting light energy into electric energy because it has highband gap. Moreover, titanium oxide has been used also for secondarybatteries such as lithium batteries, hydrogen occlusion materials,proton conductive materials, etc.

For the titanium oxide and the titanium oxide type composite oxidesapplied to various uses as described above, a great number of functionsare required. For example, when the titanium oxide is used as acatalyst, not only activity to a main reaction but also selectivity,mechanical strength, heat resistance, acid resistance and durability arerequired. When the titanium oxide is used as a decorative material, notonly ultraviolet screening effect but also smoothness, touch,transparency, etc. are required.

When the titanium oxide is used as a coating material, more improvedfilm forming properties, adhesion properties, film hardness, mechanicalstrength, abrasion resistance, etc. are required in addition totransparency and high refractive index.

From the above viewpoints, nano-tubular crystalline titanium oxide hasreceived attention, and for example, nano-tubular crystalline titaniahaving high specific surface area has been proposed in Japanese PatentLaid-Open Publication No. 152323/1998.

In this publication, it is disclosed that a crystalline titania powderis contacted with an alkali and then if necessary subjected to heat(calcining) treatment to prepare nano-tubular crystalline titania.However, even if the process described in this publication, e.g., aprocess described in the working example, is faithfully carried out,spherical particles or agglomerated particles are produced in additionto tubular particles and they are contained in the resulting crystallinetitania particles, so that the yield of nano-tubular crystalline titaniais low. Moreover, because the amount of residual sodium is large,sufficient performance of a catalyst, a catalyst carrier, aphotocatalyst or the like cannot be obtained, and in some cases, anyperformance is not exhibited at all. Thus, there are many problems inthis process.

Under such circumstances, the present inventors have earnestly studied aprocess for preparing tubular crystalline titanium oxide particles, andas a result, they have found that in Japanese Patent Laid-OpenPublication No. 152323/1998, a powder of crystalline titanium oxide,particularly a powder (crystalline titania powder) obtained by calcininga powder prepared by a sol-gel process at a high temperature, is used asa starting material, but by the use of the powder as a startingmaterial, desired tubular crystalline titanium oxide particles are notobtained. The present inventors have further studied, and as a result,they have found that hydrothermal treatment of a titanium oxide sol, inwhich particles of specific particle diameters are dispersed, in thepresence of an alkali makes it possible to obtain tubular titanium oxideparticles in an extremely high yield without producing agglomerates orspherical particles.

Photoelectric Conversion Materials

It is also known that titanium oxide is used for semiconductors forphotoelectric conversion materials of solar cells. Ordinary solar cellsare constituted in the following manner. First, a semiconductor film fora photoelectric conversion material, on which a photosensitizer has beenadsorbed, is formed as an electrode on a support such as a glass platehaving been coated with a transparent conductive film, then anothersupport such as a glass plate having been coated with a transparentconductive film as a counterpart electrode is arranged, and anelectrolyte is enclosed between these electrodes.

When the photosensitizer adsorbed on the semiconductor for aphotoelectric conversion material is irradiated with sunlight, thephotosensitizer absorbs light of visible region to excite electrons inthe photosensitizer. The thus excited electrons move to thesemiconductor, then pass through the transparent conductive glasselectrode and move to the counterpart electrode. The electrons havingmoved to the counterpart electrode reduce the oxidation-reduction system(specifically, solvent, ionic compound, etc. contained in theelectrolyte) in the electrolyte. On the other hand, the photosensitizerfrom which the electrons have moved to the semiconductor is in a stateof oxidant, and this oxidant is reduced by the oxidation-reductionsystem in the electrolyte and thereby returns to the original state. Theelectrons continuously flow in this manner, whereby the solar cell usingthe semiconductor for a photoelectric conversion material is driven.

As the photoelectric conversion material, a material wherein aphotosensitizing dye having absorption in the visible light region isadsorbed on a semiconductor surface is employed. For example, a solarcell having a layer of a color developing agent such as a transitionmetal complex on a surface of a metal oxide semiconductor is describedin Japanese Patent Laid-Open-Publication No. 220380/1989. In NationalPublication of International Patent No. 504023/1993, a solar cell havinga layer of a photosensitizing dye such as a transition metal complex ona surface of a titanium oxide semiconductor layer doped with metallicion is disclosed.

In order to enhance photoelectric conversion efficiency, it is importantfor the solar cells mentioned above that moving of electrons from thelight-absorbed and excited photosensitizing dye layer to the titaniafilm is rapidly carried out. If the moving of electrons is not carriedout rapidly, recombination of a ruthenium complex with the electronstakes place to lower the photoelectric conversion efficiency.

In order to solve such a problem, the present applicant has proposednovel photovoltaic cells in Japanese Patent Laid-Open Publication No.339867/1999, Japanese Patent Laid-Open Publication No. 77691/2000,Japanese Patent Laid-Open Publication No. 155791/2001 and JapanesePatent Application No. 123065/2001. However, photovoltaic cells havinghigher photoelectric conversion efficiency are desired.

Photocatalysts

Recently, articles utilizing photocatalytic action of titania havereceived attention. For example, tiles having titania films formed ontheir surfaces, curtains containing titania and deodorants whereintitania is supported on activated carbon or zeolite are on the marketand have been popular.

These articles are all aiming at antifouling, antibacterial ordeodorizing effect by decomposing contaminants, bacteria or odorousmatters adhering onto their surfaces utilizing the photocatalytic actionof titania.

It is said that when titania particles are irradiated with ultravioletrays, electrons or holes are produced inside the particle and they arediffused onto the particle surface and function as an oxidizing agent ora reducing agent, that is, the photocatalytic action of titania is dueto the oxidative effect or the reducing effect.

The titania coating film having such photocatalytic action needs to havea large thickness in order to increase photocatalytic activity. Further,in order that the electrons or the holes produced inside the particle bythe light irradiation move rapidly to the surface of the coating film,the coating film needs to have denseness. Therefore, high-temperaturetreatment is carried out in the film formation process to promote fusionbonding of particles, whereby denseness of the resulting coating film isincreased and hardness thereof is also increased. However, if thetreating temperature is raised, the crystal structure of titania changesfrom anatase type to rutile type, and there is brought about a problemthat the photocatalytic activity is lowered. Moreover, there is anotherproblem that it is difficult to form the titania coating film having thephotocatalytic action on a material having no heat resistance, such asglass, plastic, wood, fiber or cloth, because the coating film istreated at a high temperature in the film forming process.

On this account, an attempt to use titania particles having beensubjected to high-temperature treatment in advance was made. The titaniaparticles, however, have a disadvantage that when they are subjected tohigh-temperature treatment, they come to have large diameters, highrefractive index and wide light scattering, and therefore, a film ofhigh transparency cannot be obtained.

Under such circumstances, the present inventors have earnestly studied,and as a result, they have found that the above problems of thephotovoltaic cells and the photocatalysts can be all solved by the useof tubular titanium oxide particles of the present invention. Based onthe finding, the present invention has been accomplished.

It is an object of the present invention to provide a process forpreparing tubular titanium oxide particles useful as catalysts, catalystcarriers, adsorbents, photocatalysts, decorative materials, opticalmaterials, photoelectric conversion materials, etc., and tubulartitanium oxide particles. It is another object of the present inventionto provide photovoltaic cells and photocatalysts using the tubulartitanium oxide particles.

SUMMARY OF THE INVENTION

One embodiment of the process for preparing tubular titanium oxideparticles according to the present invention comprises:

subjecting a water dispersion sol, which is obtained by dispersing (i)titanium oxide particles and/or (ii) titanium oxide type composite oxideparticles comprising titanium oxide and an oxide other than titaniumoxide in water, said particles having an average particle diameter of 2to 100 nm, to hydrothermal treatment in the presence of an alkali metalhydroxide.

It is preferable to carry out reduction treatment (including nitridingtreatment) after the hydrothermal treatment.

In the present invention, the hydrothermal treatment may be carried outin the presence of ammonium hydroxide and/or an organic base togetherwith the alkali metal hydroxide.

Another embodiment of the process for preparing tubular titanium oxideparticles according to the present invention comprises:

subjecting a water dispersion sol, which is obtained by dispersing (i)titanium oxide particles and/or (ii) titanium oxide type composite oxideparticles comprising titanium oxide and an oxide other than titaniumoxide in water, said particles having an average particle diameter of 2to 100 nm, to hydrothermal treatment in the presence of an alkali metalhydroxide and optionally ammonium hydroxide and/or an organic base, and

then further subjecting the water dispersion sol to hydrothermaltreatment in the presence of cation (including proton) other than alkalimetal cation.

A further embodiment of the process for preparing tubular titanium oxideparticles according to the present invention comprises:

subjecting a water dispersion of titanium oxide particles and/ortitanium oxide type composite oxide particles comprising titanium oxideand an oxide other than titanium oxide, said particles having an averageparticle diameter of 2 to 100 nm, to hydrothermal treatment in thepresence of an alkali metal hydroxide, and

then subjecting the water dispersion to reduction treatment (includingnitriding treatment).

In this process, ammonium hydroxide and/or one or more organic bases maybe allowed to be present together with the alkali metal hydroxide.

In this process, further, after the hydrothermal treatment in thepresence of ammonium hydroxide and/or one or more organic bases togetherwith the alkali metal hydroxide, the water dispersion may be treated inthe presence of cation other than alkali metal cation or proton.

The titanium oxide particles according to the present invention areobtained by the above-mentioned process and have a sodium content of notmore than 0.1% by weight in terms of Na₂O.

Another embodiment of the tubular titanium oxide particles according tothe present invention is represented by the following compositionalformula (1):Ti_(a)M_(b)O_(x)N_(y)  (1)wherein a and b are numbers satisfying the conditions of a+b=1 andb=0˜0.2, x and y are numbers satisfying the conditions of 1≦x+y<2, 1≦x<2and 0≦y<0.2, and M is an element other than Ti, and

contains titanium oxide as a main component.

The tubular titanium oxide particles preferably have an outer diameter(D_(out)) of 5 to 40 nm, an inner diameter (D_(in)) of 4 to 20 nm, atube thickness of 0.5 to 10 nm, a length (L) of 50 to 1000 nm and alength (L)/outer diameter (D_(out)) ratio (L/D_(out)) of 10 to 200.

The element M other than titanium oxide is preferably one or moreelements selected from Group Ia, Group Ib, Group IIa, Group IIb, groupIIIa, Group IIIb, Group IVa, Group IVb, Group Va, Group Vb, Group VIa,Group VIb, Group VIIa and Group VIII of the periodic table, and isparticularly preferably one or more elements selected from Si, Zr, Zn,Al, Ce, Y, Nd, W, Fe and Sb.

The photovoltaic cell according to the present invention has a metaloxide semiconductor film containing the above-mentioned tubular titaniumoxide particles.

The photocatalyst according to the present invention uses theabove-mentioned tubular titanium oxide particles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a transmission type electron microscope photograph oftubular titanium oxide particles obtained in the present invention; and

FIG. 2 is a schematic sectional view of one embodiment of a photovoltaiccell according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The best mode for carrying out the present invention is described indetail hereinafter.

Process for Preparing Tubular Titanium Oxide Particles

The process for preparing tubular titanium oxide particles according tothe present invention comprises:

subjecting a water dispersion sol, which is obtained by dispersing (i)titanium oxide particles and/or (ii) titanium oxide type composite oxideparticles in water, to hydrothermal treatment in the presence of analkali metal hydroxide.

(i) Titanium Oxide Particles and/or (ii) Titanium Oxide Type CompositeOxide Particles

In the present invention, titanium oxide particles and/or titanium oxidetype composite oxide particles which contain hydroxides or hydrates areused as starting materials. These particles have an average particlediameter of 2 to 100 nm, preferably 5 to 80 nm, and are usually used inthe form of a water dispersion sol.

When the average particle diameter is in the above range, a stable waterdispersion sol is obtained, and tubular titanium oxide particles havingexcellent monodispersibility can be prepared in an extremely high yield.If the average particle diameter is smaller than the lower limit of theabove range, it is difficult to obtain a stable water dispersion sol.Even if the average particle diameter is made larger than the upperlimit of the above range, it is difficult to obtain tubular titaniumoxide particles which are more excellent in the yield of the resultingtubular titanium oxide or the monodispersibility, and the particledispersibility is sometimes lowered or the preparation of particles or asol sometimes requires much time and labor.

In the present invention, the above particles are dispersed in water toprepare a water dispersion sol, and the water dispersion sol isemployed. In the sol, an organic solvent such as an alcohol may becontained, when needed.

Although the concentration of the water dispersion sol of the titaniumoxide particles and/or the titanium oxide type composite oxide particlescomprising titanium oxide and an oxide other than titanium oxide is notspecifically restricted, it is in the range of preferably 2 to 50% byweight, more preferably 5 to 40% by weight, in terms of an oxide. Whenthe concentration is in this range, the sol is stable, and the particlesare not agglomerated in the alkali treatment. Hence, tubular titaniumoxide particles can be efficiently prepared. If the concentration islower than the lower limit of the above range, production of tubulartitanium oxide takes a long time because of too low concentration, orthe yield of the resulting tubular titanium oxide is low. If theconcentration is higher than the upper limit of the above range,stability of the water dispersion sol is lowered, or the resultingtubular titanium oxide is sometimes agglomerated because of highconcentration in the alkali treatment.

In the present invention, the titanium oxide particles may be usedsingly, or the titanium oxide type composite oxide particles comprisingtitanium oxide and an oxide other than titanium oxide may be used, or amixture of both the particles may be used.

As the oxide other than titanium oxide, an oxide of one or more elementsselected from Group Ia, Group Ib, Group IIa, Group IIb, group IIIa,Group IIIb, Group IVa, Group IVb, Group Va, Group Vb, Group VIa, GroupVIb, Group VIIa and Group VIII of the periodic table is preferable.Specific examples of such oxides include SiO₂, ZrO₂, ZnO, Al₂O₃, CeO₂,Y₂O₃, Nd₂O₃, WO₃, Fe₂O₃, Sb₂O₅, CeO₂, CuO, AgO, AuO, Li₂O, SrO, BaO,RuO₂.

If the above oxide is contained and if the oxide is an alkali-solubleoxide, tubular titanium oxide particles are particularly easilyproduced. If the oxide is an alkali-slightly soluble oxide, the oxideremains in the resulting tubular titanium oxide particles and can imparta function of a composite oxide, such as solid acid catalytic functionor ion exchange function, to the resulting tubular titanium oxideparticles.

Of the above oxides, SiO₂, ZrO₂, ZnO, Al₂O₃, CeO₂, Y₂O₃, Nd₂O₃, WO₃,Fe₂O₃ and Sb₂O₅ are particularly preferable in the present invention.When these oxides are contained, yield of tubular titanium oxide isextremely high, and by virtue of the remaining oxides, ultravioletabsorption region, dielectric constant, photocatalytic activity, protonconductivity, solid acid property, etc. of the resulting tubulartitanium oxide can be controlled. Moreover, heat stability and chemicalstability can also be controlled.

The content of the oxide other than titanium oxide in the titanium oxidetype composite oxide particles varies depending upon whether the oxideis alkali-soluble or alkali-slightly soluble, but it is in the range ofpreferably 1 to 50% by weight, more preferably 2 to 25% by weight. Whenthe content thereof is in this range, tubular titanium oxide particlescan be prepared in a high yield.

If the content of the oxide other than titanium oxide is higher than theupper limit of the above range, yield of the tubular titanium oxide issometimes lowered or spherical or needle-like particles are sometimesproduced even in case of an alkali-soluble oxide, and in case of analkali-slightly soluble oxide, tubular titanium oxide is not producedoccasionally.

The process for preparing the water dispersion sol wherein the aboveparticles are dispersed is not specifically restricted, but a titaniumoxide sol and a titanium oxide type composite oxide sol disclosed inJapanese Patent Laid-Open Publication No. 283817/1987, Japanese PatentLaid-Open Publication No. 185820/1988, Japanese Patent Laid-OpenPublication No. 255532/1990, etc., which were applied by the presentapplicant, are particularly preferably employed. For example, hydrogenperoxide is added to a titania sol or a titania gel to dissolve thetitania sol or the titania gel, then the resulting solution is mixedwith a titanium oxide sol, a titanium hydroxide sol, a sol of aninorganic oxide other than titanium oxide or an inorganic hydroxide sol,and the mixture is heated, whereby the water dispersion sol can beprepared.

For preparing titanium oxide particles or titanium oxide type compositeoxide particles used in the process for preparing tubular titanium oxideparticles according to the invention, it is preferable to useperoxotitanic acid as a titanium oxide source. The titanium oxideparticles or the titanium oxide type composite oxide particles obtainedby the use of peroxotitanic acid have uniform particle diameters, andhence a stable water dispersion sol can be obtained.

An example of the process for preparing a water dispersion (sol) oftitanium oxide particles or a water dispersion (sol) of titanium oxidetype composite oxide particles using peroxotitanic acid is given below.

(a) Step of Preparing Gel or Sol of Orthotitanic Acid

First, a titanium compound is hydrolyzed by a hitherto known process toprepare a sol or a gel of orthotitanic acid.

The gel of orthotitanic acid can be obtained by using a titanic salt,such as titanium chloride, titanium sulfate or titanyl sulfate, as atitanium compound, adding an alkali to an aqueous solution of thetitanic salt to neutralize the solution and washing the solution.

The sol of orthotitanic acid can be obtained by passing an aqueoussolution of a titanic salt through an ion exchange resin to remove anionor by adding an acid or an alkali to an aqueous solution and/or anorganic solvent solution of titanium alkoxide, such as titaniumtetramethoxide, titanium tetraethoxide or titanium tetraisopropoxide, toperform hydrolysis.

The titanium salt aqueous solution to be subjected to neutralization orhydrolysis preferably has pH of 7 to 13. If pH of the titanium saltaqueous solution is in this range, a desired gel or sol can be obtained.If pH of the titanium salt aqueous solution is out of the above range,the later-described specific surface area of the gel or sol sometimesbecomes too low, and production of tubular titanium oxide, particularlycrystalline titanium oxide, tends to be lowered.

The temperature for the neutralization or the hydrolysis is in the rangeof preferably 0 to 40° C., particularly preferably 0 to 30° C. When thetemperature is in this range, it is possible to efficiently producecrystalline tubular titanium oxide particles. If the temperature for theneutralization or the hydrolysis is out of the above range, productionof tubular titanium oxide, particularly crystalline tubular titaniumoxide, tends to be lowered.

The orthotitanic acid particles in the resulting gel or sol arepreferably amorphous.

(b) Step of Preparing Water Dispersion Sol of Titanium Oxide FineParticles

Subsequently, to the gel or sol of orthotitanic acid or a mixturethereof is added hydrogen peroxide to dissolve orthotitanic acid andthereby prepare a peroxotitanic acid aqueous solution. Then, thesolution is aged at a high temperature to prepare a water dispersion solof titanium oxide fine particles.

In the preparation of the peroxotitanic acid aqueous solution, the gelor sol of orthotitanic acid or a mixture thereof is preferably heated orstirred according to necessity. If the concentration of orthotitanicacid is too high, a long time is required for dissolving the acid, andbesides an undissolved gel is precipitated or the resultingperoxotitanic acid aqueous solution becomes viscous. Therefore, the TiO₂concentration is preferably not more than about 10% by weight, morepreferably not more than about 5% by weight.

The amount of hydrogen peroxide added is such an amount that theH₂O₂/TiO₂ (orthotitanic acid: in terms of TiO₂) weight ratio is not lessthan 1, and in this case, the orthotitanic acid can be completelydissolved. If the H₂O₂/TiO₂ weight ratio is less than 1, theorthotitanic acid cannot be dissolved completely, and the unreacted gelor sol sometimes remains. As the H₂O₂/TiO₂ weight ratio becomes higher,the rate of dissolving the orthotitanic acid is increased and thereaction is completed in a shorter period of time. However, even ifhydrogen peroxide is used excessively, the unreacted hydrogen peroxideremains in the system, and it is economically disadvantageous. Whenhydrogen peroxide is used in the above amount, the orthotitanic aciddissolves in about 0.5 to 20 hours.

Then, the resulting solution is aged at a high temperature of not lowerthan 50° C. to prepare a water dispersion sol of titanium oxide fineparticles.

The resulting water dispersion sol of titanium oxide fine particles canbe subjected to hydrothermal treatment in the temperature range of 50 to300° C., preferably 80 to 250° C., optionally in the presence ofammonium hydroxide and/or an organic base. As the organic base, the sameorganic base as described later can be employed.

It is desirable to add the ammonium hydroxide and/or the organic base insuch an amount that pH of the dispersion becomes 8 to 14, preferably 10to 13.5, at room temperature.

When the hydrothermal treatment is carried out under the conditions ofthe above temperature and the above pH of the dispersion, crystallinityof the finally obtained tubular titanium oxide and yield thereof tend tobe enhanced.

In the above steps (a) and (b), it is possible that a peroxotitanic acidaqueous solution is prepared by the use of a titanium hydride finepowder as a titanium compound and from the peroxotitanic acid aqueoussolution, a water dispersion sol of titanium oxide fine particles isprepared in the same manner as described above.

In this case, if the titanium hydride fine powder is dispersed in water,the resulting dispersion can be substituted for the gel or sol oforthotitanic acid prepared in the step (a).

When the titanium hydride fine powder is dispersed in water, the TiO₂concentration is preferably not more than about 10% by weight, morepreferably not more than about 5% by weight. Also when the titaniumhydride fine powder is used instead of the orthotitanic acid, the amountof hydrogen peroxide added is such an amount that the H₂O₂/TiO₂(titanium hydride: in terms of TiO₂) weight ratio becomes not less than1 similarly to the above. The water dispersion of the titanium hydridefine powder may be heated to not lower than about 50° C. or stirred,when needed.

A water dispersion (sol) of titanium oxide type composite oxideparticles can be prepared in the following manner. Hydrogen peroxide isadded to the gel or sol of orthotitanic acid or a mixture thereof togive a peroxotitanic acid aqueous solution wherein the orthotitanic acidis dissolved, and with this aqueous solution, a salt of inorganiccompound particles of an element other than titanium (e.g., silicaparticles, silica sol, alumina particles, zirconia particles),alkoxisilane, metal alkoxide, zirconium chloride, magnesium chloride orthe like is mixed, then the mixture is heated, and hydrothermaltreatment is carried out in the temperature range of 50 to 300° C.,preferably 80 to 250° C., optionally in the presence of ammoniumhydroxide and/or an organic base, similar to the aforesaid step (b).

(c) Hydrothermal Treatment Step

The water dispersion sol of (i) titanium oxide particles and/or (ii)titanium oxide type composite oxide particles prepared as above was thensubjected to hydrothermal treatment in the presence of an alkali metalhydroxide.

Examples of the alkali metal hydroxides employable herein include LiOH,NaOH, KOH, RbOH, CsOH and mixtures thereof. Of these, particularlypreferable are NaOH, KOH and a mixture thereof because the yield oftubular titanium oxide particles is high.

The amount of the alkali metal hydroxide added is desirably such anamount that the molar ratio (A_(M))/(T_(M)) of the number of moles(A_(M)) of the alkali metal hydroxide to the number of moles (T_(M)) ofTiO₂ in the titanium oxide particles or the titanium oxide typecomposite oxide particles contained in the sol is in the range of 1 to30, preferably 2 to 25. When the molar ratio (A_(M))/(T_(M)) is in thisrange, tubular titanium oxide particles can be prepared efficiently. Ifthe molar ratio (A_(M))/(T_(M)) is lower than the lower limit of theabove range, crystallization of the titanium oxide particles or thetitanium oxide type composite oxide particles hardly takes place, andhence tubular titanium oxide particles are not obtained. If the molarratio (A_(M))/(T_(M)) is higher than the upper limit of the above range,plate titanium oxide particles tend to be increased to lower yield oftubular titanium oxide particles.

In the present invention, the hydrothermal treatment may be carried outin the presence of ammonium hydroxide and/or an organic base togetherwith the alkali metal hydroxide.

Examples of the organic bases include quaternary ammonium salts, such astetramethylammonium salt, hydroxides, and amines, such asmonoethanolamine, diethanolamine and triethanolamine.

When the ammonium hydroxide and/or the organic base is allowed tocoexist, the amount thereof is desirably such an amount that the ratio[(A_(M))+(OB_(M))]/(T_(M)) of the total number of moles[(A_(M))+(OB_(M))] of the ammonium hydroxide and/or the organic base tothe number of moles (T_(M)) of TiO₂ becomes 1 to 30, preferably 2 to 25.When the ammonium hydroxide and/or the organic base is allowed tocoexist, further, the molar ratio of (A_(M)):(OB_(M)) is desirably inthe range of 0:1 to 1:1, preferably 0:1 to 0.5:1. When the ammoniumhydroxide and/or the organic base is allowed to coexist in this manner,the amount of the alkali metal hydroxide used can be decreased, andhence, the amount of alkali metal impurities contained in the tubulartitanium oxide fine particles can be decreased. Consequently, it becomespossible to favorably use the tubular titanium oxide particles ascatalysts (carriers) or photocatalysts.

In the presence of the alkali metal hydroxide and if necessary theammonium hydroxide and/or the organic base, the water dispersion sol oftitanium oxide particles and/or titanium oxide type composite oxideparticles is subjected to hydrothermal treatment in the temperaturerange of 50 to 350° C., preferably 80 to 250° C. When the temperature isin this range, tubular titanium oxide particles can be preparedefficiently. If the hydrothermal treatment temperature is lower than thelower limit of the above range, a long time is required for theproduction of tubular titanium oxide fine particles, or the yield of thetubular titanium oxide fine particles is low. Even if the hydrothermaltreatment temperature is higher than the upper limit of the above range,the rate of production of the tubular titanium oxide fine particles isnot increased or the yield does not become higher, and extra heat energyis consumed.

Then, the resulting tubular titanium oxide fine particles may besubjected to washing, when needed. The washing method is notspecifically restricted provided that the amount of an alkali metal orthe like can be decreased, and various methods hitherto known, such asdehydration filtration method, ultrafiltration membrane method, ionexchange resin method, electrodialysis method and reverse osmosismethod, are adoptable. The washing may be carried out by the use ofacids such as hydrochloric acid and nitric acid.

In the present invention, the hydrothermal treatment is carried out inthe presence of the alkali metal hydroxide and if necessary ammoniumhydroxide and/or organic base, then washing is carried out when needed,and thereafter, the resulting particle dispersion may be furthersubjected to hydrothermal treatment in the presence of cation (includingproton) other than alkali metal cation.

That is to say, another embodiment of the process for preparing tubulartitanium oxide particles according to the invention comprises:

subjecting the water dispersion sol of (i) titanium oxide particlesand/or (ii) titanium oxide and an oxide other than titanium oxide tohydrothermal treatment in the presence of an alkali metal hydroxide andif necessary ammonium hydroxide and/or an organic base (first step), and

then further subjecting the water dispersion sol to hydrothermaltreatment in the presence of cation (including proton) other than alkalimetal cation (second step).

The hydrothermal treatment temperature in each step is in the range of50 to 350° C., preferably 80 to 250° C.

In the hydrothermal treatment of the first step, the types and theamounts of ammonium hydroxide and the organic base and the treatingconditions in the presence of the metal hydroxide used are the same asthose previously described. After the hydrothermal treatment of thefirst step is carried out in the presence of the alkali metal hydroxide,the resulting dispersion may be washed to remove liberating alkali metalimpurities in the dispersion and on the particle surfaces, when needed.

The washing method is not specifically restricted provided that theamount of an alkali metal or the like can be decreased, and variousmethods hitherto known, such as dehydration filtration method,ultrafiltration membrane method, ion exchange resin method,electrodialysis method and reverse osmosis method, are adoptable. Thewashing can be carried out by the use of acids such as hydrochloric acidand nitric acid.

The hydrothermal treatment of the second step is carried out in thepresence of cation (including proton) other than the alkali metalcation. Examples of cation sources include acids, salts containing noalkali metal, and organic bases. Examples of the acids include mineralacids, such as hydrochloric acid, nitric acid and sulfuric acid; andorganic acids, such as acetic acid, oxalic acid, citric acid, glycolicacid, glycidic acid, malonic acid and maleic acid. Examples of the saltscontaining no alkali metal include ammonium salts, such as ammoniumchloride, ammonium nitrate, ammonium sulfate and ammonium acetate.Examples of the organic bases include ammonium hydroxide, quaternaryammonium salts such as tetramethylammonium salt, hydroxides containingthe ammonium ion, and amines such as monoethanolamine, diethanolamineand triethanolamine.

The acid, the salt containing no alkali metal or the organic basementioned above is used in such an amount that the molar ratio(P_(M)/T_(M)) of the number of moles (P_(M)) of the acid or the saltcontaining no alkali metal or the organic base to the number of moles(T_(M)) of TiO₂ in the titanium oxide particles or the titanium oxidetype composite oxide particles is in the range of 1 to 30, preferably 2to 15.

For adding proton, it is possible to contact the dispersion with an ionexchange resin or the like. The ion exchange resin is preferably ahydrogen type cation exchange resin. As the ion exchange resin, anamphoteric ion exchange resin may be used, or an anion exchange resinmay be used in combination, when needed. By the treatment using theorganic acid, tubular titanium oxide containing decreased amount of analkali metal, particularly Na, can be obtained without deterioration ofthe crystalline state.

Through the hydrothermal treatment of the second step, the crystallinestate of the resulting tubular titanium oxide can be enhanced withoutcalcining at high temperatures.

Further, the amount of residual alkali metal in the titanium oxideparticles is decreased, and consequently, crystalline tubular titaniumoxide particles having high crystallinity, which are employable forcatalysts, catalyst carriers, photocatalysts, decorative materials,optical materials, photoelectric conversion material, etc., can beprepared.

The hydrothermal treatment of the second step in the presence of cationother than alkali metal cation may be repeated plural times.

In comparison of the tubular titanium oxide particles obtained in thehydrothermal treatment of the second step with the tubular titaniumoxide particles obtained in the hydrothermal treatment of the firststep, the particle properties such as particle shape and specificsurface area are the same except that the particles obtained in thesecond step contain smaller amount of impurities and have highercrystallinity than the particles obtained in the first step.

After the hydrothermal treatment, drying is carried out. There is nospecific limitation on the drying method, and hitherto known methods areadoptable. For example, any of air drying, heating and freeze drying isadoptable.

After the drying, reduction treatment may be carried out, when needed.

(d) Reduction Treatment

By carrying out reduction treatment after drying, the later-describedreduction type tubular titanium oxide particles can be obtained. Thereduction treatment can be carried out on any of the particles havingbeen subjected to one hydrothermal treatment and the particles havingbeen subjected to two or more hydrothermal treatments.

The atmosphere of the reduction treatment is not specifically restrictedprovided that the tubular titanium oxide particles represented by theaforesaid formula (1) (sometimes referred to as “reduction type tubulartitanium oxide” hereinafter) can be obtained, but it is preferable tocarry out the reduction treatment in (A) an inert gas atmosphere, under(B) reduced pressure or in (C) a reducing gas atmosphere.

Examples of the inert gases include N₂, He, Ne, Ar, Kr, Xe and Rn.

When the reduction treatment is carried out under reduced pressure, thedegree of reduced pressure varies depending upon the treatingtemperature and the treating time, but it has only to be lower thanatmospheric pressure.

Examples of the reducing gases employable herein include nitrogencompounds having reducing ability, such as ammonia, amine, hydrazine andpyridine; and hydrocarbons, such as methane, ethane and propane.

The reduction treatment temperature is desirably in the range of 100 to700° C., preferably 200 to 500° C.

When the reduction treatment temperature is in the above range,reduction type tubular titanium oxide particles aimed by the presentinvention can be prepared. If the reduction treatment temperature is toolow, reactions, such as elimination of lattice oxygen of the tubulartitanium oxide particles and substitution of the eliminated oxygen withnitrogen atom, hardly take place, and therefore, the reduction typetubular titanium oxide of the invention is not obtained occasionally.

If the reduction treatment temperature is too high, elimination ofoxygen proceeds too much, and the crystalline state is deteriorated atthe same time. Hence, sufficient conductivity, photocatalyticperformance, catalytic performance and adsorption power, and desiredoptical properties and photoelectric conversion properties cannot beobtained occasionally.

The reduction type tubular titanium oxide particles thus obtained havean alkali content of not more than 0.1% by weight, preferably not morethan 0.05% by weight, particularly preferably not more than 0.01% byweight, in terms of Na₂O.

Particularly, the reduction type tubular titanium oxide particles havingan alkali content of not more than 0.01% by weight in terms of Na₂O areuseful not only as catalyst carriers and adsorbents but also asconductive materials, photocatalysts, photoelectric conversionsemiconductor materials and optical materials.

Tubular Titanium Oxide Particles

The tubular titanium oxide particles of the invention are those obtainedby the preparation process described above.

The tubular titanium oxide particles have an outer diameter (D_(out)) of5 to 40 nm, an inner diameter (D_(in)) of 4 to 30 nm, a tube thicknessof 0.5 to 20 nm, a length (L) of 25 to 1000 nm and a length (L)/outerdiameter (D_(out)) ratio (L/D_(out)) of 5 to 200.

In FIG. 1, an electron microscope photograph of the tubular titaniumoxide particles is shown.

The outer diameter (D_(out)), the inner diameter (D_(in)) and the length(L) are determined by taking a transmission type electron microscopephotograph of the tubular titanium oxide particles, measuring values of100 particles and calculating average values. The inner diameter(D_(in)) can be determined from a line that forms a contrast borderobserved inside the line for determining an outer diameter.

The composition of the tubular titanium oxide particle depends uponcomposition of the starting titanium oxide particle used. When thestarting material contains an oxide other than titanium oxide, theresulting particles also contain the oxide other than titanium oxide inthe same proportion.

Examples of crystal types (crystal forms) of the tubular titanium oxideparticles include anatase type, rutile type and brookite type. Thecrystalline state of the resulting particle varies depending upon theheat treatment, the type of the starting titanium oxide sol, etc.

Especially when the alkali treatment is carried out in two steps and inthe second step or thereafter hydrothermal treatment is carried out inthe presence of cation containing no alkali metal, the resulting tubulartitanium oxide particles have an alkali content of not more than 0.1% byweight, preferably not more than 0.05% by weight, particularlypreferably not more than 0.01% by weight, in terms of Na₂O, and they aredesirable.

Reduction Type Tubular Titanium Oxide Particles

One embodiment of the tubular titanium oxide particles according to theinvention is represented by the following compositional formula (1) andcontains titanium oxide as a main component. Since this tubular titaniumoxide particle is not a complete oxide, it is sometimes referred to as a“reduction type tubular titanium oxide particle”.Ti_(a)M_(b)O_(x)N_(y)  (1)wherein a and b are numbers satisfying the conditions of a+b=1 andb=0˜0.2, x and y are numbers satisfying the conditions of 1≦x+y<2, 1≦x<2and 0≦y<0.2, and M is an element other than Ti.

In the formula (1), the proportion b of the element M other than Ti isin the range of 0 to 0.2, preferably 0 to 0.15.

If the proportion b of the element M other than Ti exceeds 0.2, tubulartitanium oxide is not obtained occasionally though it depends upon thetype of the element M.

The proportions of oxygen atom (O) and nitrogen atom (N) are as follows.That is to say, 1≦x+y<2 is preferable, and 1.2≦x+y<1.9 is morepreferable; 1≦x<2 is preferable, and 1.2≦x<1.9 is more preferable; and0≦y<0.2 is preferable, and 0≦y≦0.1 is more preferable.

When x+y is in the above range, the tubular titanium oxide particlebecomes a non-stoichiometric substance, namely, not a complete oxide buta partially reduced low oxide, and this substance has lowersemiconductor properties as compared with titanium oxide (TiO₂), thatis, the tubular titanium oxide particle itself has conductivity.Further, the molecular orbital greatly varies, and thereby lightabsorption properties are changed. Therefore, tubular titanium oxidecapable of absorbing not only ultraviolet rays but also visible lightcan be obtained.

When x+y is 2, this particle is titanium oxide or titanium oxide typecomposite oxide, so that there is no oxygen defect (this particle has atitanium oxidation number of 4 and is different from reduced titaniumhaving a titanium oxidation number of less than 4), and an effect ofenhancing necessary conductivity or an effect of widening visibleabsorption region cannot be obtained.

When x+y is less than 1, the crystalline state is lowered or cannot bemaintained in some cases.

It is difficult to obtain reduction type titanium oxide having y of notless than 0.2, and even if such an oxide is obtained, conductivity orvisible light absorption power is not increased.

The reduction type tubular titanium oxide particles of the inventionsometimes contain hydrogen atom (H) in addition to the aforesaidelements and components.

The outer diameter (D_(out)), the inner diameter (D_(in)), the length(L) and the (L)/(D_(out)) ratio of the reduction type tubular titaniumoxide particles are the same as those of the aforesaid tubular titaniumoxide particles (not reduction type). More specifically, the innerdiameter (D_(in)) is in the range of 4 to 20 nm, preferably 4 to 15 nm;the tube thickness is in the range of 0.5 to 10 nm, preferably 0.5 to 8nm; the length (L) is in the range of 50 to 1000 nm, preferably 100 to500 nm; and the length (L)/outer diameter (D_(out)) ratio (L/D_(out)) isin the range of 10 to 200, preferably 10 to 100. The reduction typetubular titanium oxide particles having diameters, etc. of these rangesare useful as catalysts, catalyst carriers, adsorbents, photocatalysts,decorative materials, optical materials, photoelectric conversionmaterials, etc., and besides, they are effectively used for protonconductive materials, electrolyte films for fuel cells and otherconductive materials.

The element M is preferably an element (M) selected from Group Ia, GroupIb, Group IIa, Group IIb, group IIIa, Group IIIb, Group IVa, Group IVb,Group Va, Group Vb, Group VIa, Group VIb, Group VIIa and Group VIII ofthe periodic table. Examples of such elements include Si, Zr, Zn, Al,Ce, Y, Nd, W, Fe, Sb, Ce, Cu, Ag, Au, Li, Sr, Ba and Ru. Of these,particularly preferable are Si, Zr, Zn, Al, Ce, Y, Nd, W, Fe and Sb.When these elements remain as oxides, ultraviolet absorption region,dielectric constant, photocatalytic activity, proton conductivity, solidacid property, etc. of the tubular titanium oxide particles can becontrolled. The element M (element other than Ti) is derived from anoxide other than titanium oxide, which is added as a starting material.

The reduction type tubular titanium oxide particles can be prepared bysubjecting the tubular titanium oxide particles obtained in theaforesaid preparation process to reduction treatment.

Uses

The tubular titanium oxide particles of the invention can be favorablyused as catalysts, catalyst carriers, adsorbents, decorative materialsand ultraviolet light absorbing agents. Particularly, the tubulartitanium oxide particles having an alkali content of not more than 0.01%by weight in terms of Na₂O are useful as photocatalysts andphotoelectric conversion semiconductor materials.

When the tubular titanium oxide particles are used as catalysts, theyare usually used as supported type catalysts on which metals, such asplatinum, nickel and silver, are supported. Further, taking advantage oftubular form, they can be used as materials in which organic, inorganicor metal materials are inserted and which have new functions ormaterials in which magnetic materials are inserted and which havemagnetic properties.

The reduction type tubular titanium oxide particles are useful ascatalysts, adsorbents, photocatalysts, optical materials, photoelectricconversion materials, etc., and besides, they are effectively used forproton conductive materials, electrolyte films for fuel cells and otherconductive materials.

Photovoltaic Cell

The photovoltaic cell according to the present invention comprises:

a substrate having an electrode layer (1) on its surface and having ametal oxide semiconductor film (2) which is formed on a surface of theelectrode layer (1) and on which a photosensitizer is adsorbed,

a substrate having an electrode layer (3) on its surface,

both of said substrates being arranged in such a manner that theelectrode layer (1) and the electrode layer (3) face each other, and

an electrolyte layer provided between the metal oxide semiconductor film(2) and the electrode layer (3),

wherein at least one pair of substrate and electrode have transparency,and the metal oxide semiconductor film (2) contains tubular titaniumoxide particles.

Such a photovoltaic cell is, for example, a photovoltaic cell shown inFIG. 1.

FIG. 1 is a schematic sectional view of one embodiment of a photovoltaiccell of the present invention. In this embodiment, a transparentsubstrate 5 having a transparent electrode layer 1 on its surface andhaving a metal oxide semiconductor film 2 which is formed on a surfaceof the electrode layer 1 and on which a photosensitizer is adsorbed, anda substrate 6 having an electrode layer 3 having reduction catalyticability on its surface are arranged in such a manner that the electrodelayer 1 and the electrode layer 3 face each other, and between the metaloxide semiconductor film 2 and the electrode layer 3, an electrolyte 4is enclosed.

As the transparent substrate 5, a substrate having transparency andinsulating properties, such as a glass substrate or an organic polymersubstrate (e.g., PET substrate), is employable.

The substrate 6 is not specifically restricted provided that it has astrength enough to withstand its use, and not only insulatingsubstrates, such as a glass substrate and an organic polymer substrate(e.g., PET substrate), but also conductive substrates, such assubstrates of metallic titanium, metallic aluminum metallic copper andmetallic nickel, are employable.

As the transparent electrode layer 1 formed on the surface of thetransparent substrate 5, a hitherto known electrode is employable.Examples of such electrodes include tin oxide, tin oxide doped with Sb,F or P, indium oxide doped with Sn and/or F, antimony oxide, zinc oxideand precious metals.

The transparent electrode layer 1 can be formed by a hitherto knownmethod, such as a thermal decomposition method or a CVD method.

As the electrode layer 3 formed on the surface of the substrate 6, ahitherto known electrode is employable. Examples of such electrodesinclude electrode materials, such as platinum, rhodium, ruthenium metaland ruthenium oxide, electrodes obtained by plating or depositing theelectrode materials on the surfaces of conductive materials, such as tinoxide, tin oxide doped with Sb, F or P, indium oxide doped with Snand/or F and antimony oxide, and carbon electrode.

The electrode layer 3 can be formed by a hitherto known method, such asa method comprising providing the electrode on the substrate 6 by directcoating, plating or deposition, subjecting a conductive material to aconventional method such as thermal decomposition or CVD method to forma conductive layer and then plating or depositing the above electrodematerial on the conductive layer.

The substrate 6 may be a transparent substrate similarly to thetransparent substrate 5, and the electrode layer 3 may be a transparentelectrode layer similarly to the transparent electrode layer 1.

The visible light transmittance of the transparent substrate 5 and thetransparent electrode layer 1 is Preferably as high as possible, andspecifically, it is not less than 50%, particularly preferably not lessthan 90%. When the visible light transmittance is in this range, aphotovoltaic cell having high photoelectric conversion efficiency can beobtained.

Each of the transparent electrode layer 1 and the electrode layer 3preferably has a resistance value of not more than 100 Ω/cm². When theresistance value of the electrode layer is in this range, a photovoltaiccell having high photoelectric conversion efficiency can be obtained.

The metal oxide semiconductor film 2 is formed on the transparentelectrode layer 1 that is formed on the transparent substrate 5. Themetal oxide semiconductor film 2 may be formed on the electrode layer 3that is formed on the substrate 6. The thickness of the metal oxidesemiconductor film 2 is in the range of preferably 0.1 to 50 μm, morepreferably 2 to 20 μm.

In the metal oxide semiconductor film 2, the aforesaid tubular titaniumoxide particles are contained.

As the tubular titanium oxide particles, those having the aforesaidinner diameter, outer diameter, thickness and length are employed. It isdesired that the outer diameter (D_(out)) is in the range of 5 to 40 nm,preferably 10 to 30 nm, the inner diameter (D_(in)) is in the range of 4to 30 nm, preferably 5 to 20 nm, the tube thickness is in the range of 1to 20 nm, preferably 2 to 15 nm, the length (L) is in the range of 25 to1000 nm, preferably 50 to 600 nm, and the length (L)/outer diameter(D_(out)) ratio (L/D_(out)) is in the range of 5 to 200, preferably 10to 100. When the tubular oxide titanium particles having diameters, etc.of these ranges are used, a photovoltaic cell having excellentphotoelectric conversion efficiency can be produced.

If the outer diameter (D_(out)) of the tubular titanium oxide particleis less than the lower limit of the above range, the inner diameterbecomes less than 4 nm correspondingly, so that diffusion of thelater-described electrolyte is insufficient, and satisfactoryphotoelectric conversion efficiency is not obtained occasionally.

It is difficult to obtain tubular titanium oxide particles having anouter diameter (D_(out)) of more than the upper limit of the aboverange.

If the inner diameter (D_(in)) of the tubular titanium oxide particle isless than the lower limit of the above range, sufficient photoelectricconversion efficiency is not obtained occasionally, as previouslydescribed.

It is difficult to obtain tubular titanium oxide particles having aninner diameter (D_(in)) of more than the upper limit of the above range,and the density of titanium oxide in the metal oxide semiconductor filmis lowered, so that satisfactory photoelectric conversion efficiency isnot obtained occasionally.

If the tube thickness is less than the lower limit of the above range,the thickness of the crystal layer is small and the function of thesemiconductor becomes insufficient, so that satisfactory photoelectricconversion efficiency is not obtained occasionally.

If the tube thickness is more than the upper limit of the above range,the feature (effect) that the specific surface area is higher than thatof conventional crystalline titanium oxide becomes less distinct, andcorrespondingly, the adsorption amount of the spectrosensitizing dyedoes not become sufficiently large, so that the effect of increasingphotoelectric conversion efficiency sometimes becomes insufficient. Ifthe length (L) of the tubular titanium oxide particle is less than thelower limit of the above range, the number of particles in the metaloxide semiconductor film is increased to thereby increase particleboundary resistance, so that sufficient photoelectric conversionefficiency is not obtained occasionally. If the length (L) of thetubular titanium oxide particle is more than the upper limit of theabove range, diffusion of the electrolyte becomes insufficient andsatisfactory photoelectric conversion efficiency is not obtainedoccasionally, though it depends upon the inner diameter of the tube. Ifthe ratio of the length (L) of the tubular titanium oxide particle tothe outer diameter (D_(out)) thereof, i.e., (L)/(D_(out)) ratio, is lessthan the lower limit of the above range, adhesion of the resulting metaloxide semiconductor film to the electrode layer is lowered, and thestrength of the film sometimes becomes insufficient. If the(L)/(D_(out)) ratio is more than the upper limit of the above range,light scattering is increased or diffusion of the electrolyte becomesinsufficient, so that satisfactory photoelectric conversion efficiencyis not obtained occasionally.

The alkali metal content in the tubular titanium oxide particles usedfor the photovoltaic cell is preferably not more than 500 ppm, morepreferably not more than 200 ppm, particularly preferably not more than100 ppm.

If the alkali metal content is too high, the function of thesemiconductor is lowered, and the photoelectric conversion efficiencytends to be lowered with time.

The tubular titanium oxide particles used for the photovoltaic cell ofthe invention may be particles of amorphous titanium oxide, but they arepreferably particles of crystalline titanium oxide, such as anatase typetitanium oxide, brookite type titanium oxide, rutile type titaniumoxide, or their mixed crystal or eutectic crystal, and they areparticularly preferably particles of anatase type titanium oxide orbrookite type titanium oxide because of high band gap.

The crystal diameter of the anatase type titanium oxide and the brookitetype titanium oxide is in the range of preferably 1 to 50 nm, morepreferably 5 to 30 nm. When the crystal diameter is in this range, theadsorption amount of the photosensitizer is increased, and hence, aphotovoltaic cell having excellent photoelectric conversion efficiencycan be produced.

The crystal diameter of the anatase type titanium oxide primary particlecan be determined by measuring a half band width of a peak of the(1.0.1) face, followed by calculation from the Debye-Scherrer's formula.The crystal diameter of the brookite type titanium oxide primaryparticle can be determined by measuring a half band width of a peak ofthe (1.1.1) face through X-ray diffractometry, followed by calculationfrom the Debye-Scherrer's formula. If the crystal diameter of thebrookite type titanium oxide primary particle or the anatase typetitanium oxide primary particle is less than the lower limit of theabove range, electron mobility in the particle is deteriorated. If thecrystal diameter thereof is more than the upper limit of the aboverange, the adsorption amount of the photosensitizer is decreased, andthe photoelectric conversion efficiency is sometimes lowered.

In case of the eutectic crystal, crystal lattice constant, crystal formand crystal diameter can be determined by the field emission typetransmission electron microscope photograph (FE-TEM) measurement.

The metal oxide semiconductor film 2 contains a titanium oxide bindercomponent in addition to the tubular titanium oxide particles.

The titanium oxide binder component is, for example, peroxotitanic acidthat is obtained by adding hydrogen peroxide to a sol or a gel oforthotitanic acid obtained through a sol-gel process to thereby dissolvehydrated titanic acid.

Particularly, a hydrolysis polycondensate of peroxotitanic acid ispreferably employed.

The titanium oxide binder component forms a dense and uniform adsorptionlayer on the surface of the tubular titanium oxide particle. Therefore,adhesion of the resulting metal oxide semiconductor film to theelectrode can be increased. By the use of the titanium oxide bindercomponent, further, contact area of the tubular titanium oxide particlesis increased, and thereby electron mobility can be enhanced or theadsorption amount of the photosensitizer can be increased.

The weight ratio (in terms of an oxide) of the titanium oxide bindercomponent to the tubular titanium oxide particles (titanium oxide bindercomponent/tubular titanium oxide particle) in the metal oxidesemiconductor film 2 is desired to be in the range of 0.03 to 0.50,preferably 0.1 to 0.3. When the weight ratio is in this range, theadsorption amount of the photosensitizer is increased, and a desiredporous semiconductor can be obtained. If the weight ratio is less thanthe lower limit of the above range (that is, the amount of the binder issmall), visible light absorption is insufficient, and in some cases, theadsorption amount of the photosensitizer is not increased. If the weightratio is more than the upper limit of the above range (that is, theamount of the binder is large), a porous semiconductor film is notobtained occasionally, and the adsorption amount of the photosensitizeris not increased in some cases.

The metal oxide semiconductor film 2 preferably has a pore volume of 0.1to 0.8 ml/g and an average pore diameter of 2 to 250 nm. If the porevolume is less than the lower limit of the above range, the adsorptionamount of the photosensitizer is decreased. If the pore volume is morethan the upper limit of the above range, electron mobility in the filmis deteriorated to sometimes lower the photoelectric conversionefficiency. If the average pore diameter is less than the lower limit ofthe above range, the adsorption amount of the photosensitizer isdecreased. If the average pore diameter is more than the upper limit ofthe above range, electron mobility in the film is deteriorated tothereby lower the photoelectric conversion efficiency occasionally.

The metal oxide semiconductor film 2 can be prepared by the use of acoating solution for forming a metal oxide semiconductor film for aphotovoltaic cell.

In the present invention, a photosensitizer is adsorbed on the metaloxide semiconductor film 2.

The photosensitizer is not specifically restricted provided that itabsorbs light of visible region and/or infrared region and is excited.For example, organic dyes and metal complexes are employable.

Examples of the organic dyes employable herein include conventionallyknown organic dyes having functional groups, such as carboxyl group,hydroxyalkyl group, hydroxyl group, sulfone group and carboxyalkylgroup, in their molecules. More specifically, there can be mentionedxanthene, coumarin, acridine, tetraphenylmethane, quinone, Eosin Y,dibromofluorescein, fluoroescein, fluorescin, metal-free phthalocyanine,cyanine dyes, metallocyanine dyes, triphenylmethane dyes, and xanthenedyes, such as Uranin, eosin, rose bengal, Rhodamine B anddibromofluorescein. These dyes have characteristics of a high rate ofadsorption on the metal oxide semiconductor film.

Examples of the metal complexes include metal phthalocyanines, such ascopper phthalocyanine and titanyl phthalocyanine; chlorophyll; hemin;ruthenium-cis-diacquo-bipyridyl complexes, such asruthenium-tris(2,2′-bispyridyl-4,4′-dicarboxylate),cis-(SCN⁻)-bis(2,2′-bipyridyl-4,4′-dicarboxylate) ruthenium andruthenium-cis-diaquo-bis(2,2′-bipyridyl-4,4′-dicarboxoylate); porphyrinsuch as zinc-tetra (4-carboxyphenyl)porphyrin; and complexes ofruthenium, osmium, iron, zinc or the like, such as an iron-hexacyanidecomplex, as described in Japanese Patent Laid-Open Publication No.220380/1989 and National Publication of International Patent No.504023/1993. These metal complexes exhibit excellent spectrosensitizingeffect and durability.

The above organic dyes and metal complexes may be used singly or as amixture of two or more kinds, or the organic dyes and the metalcomplexes may be used in combination.

There is no specific limitation on the adsorption method of thephotosensitizer, and methods generally used are adoptable. For example,the metal oxide semiconductor film is allowed to absorb a solventsolution of the photosensitizer by dipping, spinner method, spraying orthe like and then dried. The absorption step may be repeated, whenneeded. The photosensitizer can also be adsorbed on the metal oxidesemiconductor film by contacting the solution of the photosensitizerwith the substrate while the solution is refluxed under heating.

The solvent for dissolving the photosensitizer has only to be a solventcapable of dissolving the photosensitizer, and examples of the solventsemployable include water, alcohols, toluene, dimethylformamide,chloroform, ethyl cellosolve, N-methylpyrrolidone and tetrahydrofuran.

The amount of the photosensitizer adsorbed on the metal oxidesemiconductor film is preferably not less than 50 μg based on 1 cm² ofthe specific surface area of the metal oxide semiconductor film. If theamount of the photosensitizer is small, the photoelectric conversionefficiency sometimes becomes insufficient.

The photovoltaic cell of the invention is produced by arranging themetal oxide semiconductor film 2 and the transparent electrode layer 3so that they should face each other, sealing their sides with a resin orthe like and enclosing an electrolyte 4 between the electrodes.

As the electrolyte 4, a mixture of an electrochemically active salt andat least one compound which forms an oxidation-reduction system isemployed.

Examples of the electrochemically active salts include quaternaryammonium salts such as tetrapropylammonium iodide. Examples of thecompounds which form an oxidation-reduction system include quinone,hydroquinone, iodine (I⁻/I₃ ⁻), potassium iodide, bromine (Br⁻/Br₃ ⁻)and potassium bromide.

In the present invention, a solid electrolyte may be used as theelectrolyte. Examples of the solid electrolytes employable hereininclude CuI, CuBr, CuSCN, polyaniline, polypyrrole, polythiophene,arylamine type polymers, polymers having acrylic group and/ormethacrylic group, polyvinyl carbazole, triphenyldiamine polymer,L-valine, derivative low-molecular gel, polyoligoethylene glycolmethacrylate, poly(o-methoxy aniline), poly(epichlorohydrin-Co-ethyleneoxide),2,2′,7,7′-tetrakis(N,N-di-P-methoxyphenyl-amine)-9,9′-spirobifluorene,fluorine-type ion exchange resins having proton conductivity, such asperfluorosulfonate, perfluorocarbon copolymer, andperfluorocarbonsulfonic acid. In addition thereto, polyethylene oxideand a substance obtained by forming ion pair from, for example,imidazole cation and Br⁻, BF₄ ⁻ or N—(SO₂CF₃)₂ by an ion gel process andthen adding a vinyl monomer or a PMMA monomer to perform polymerizationare also preferably employed.

When the solid electrolyte is used, the electrolyte is not scattereddifferently from a liquid electrolyte, and therefore, photoelectricconversion efficiency is not lowered even if it is used for a longperiod of time, and besides the electrolyte does not cause corrosion orthe like.

In the present invention, an electrolytic solution obtained by the useof a solvent may be used as the electrolyte 4, if desired. The solventused herein is desired to have such a low dissolving power for thephotosensitizer that the photosensitizer adsorbed on the metal oxidesemiconductor film is not desorbed and not dissolved in the solution.Examples of such solvents include water, alcohols, oligoethers,carbonates such as propion carbonate, phosphoric acid esters,dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone,N-vinylpyrrolidone, sulfur compounds such as sulfolane 66, ethylenecarbonate, and acetonitrile.

Coating Solution for Forming Metal Oxide Semiconductor Film forPhotovoltaic Cell

For forming the metal oxide semiconductor film 2 used in the invention,peroxotitanic acid as a precursor of a titanium oxide binder componentand/or a titanium oxide particle dispersion sol having an averageparticle diameter of not more than 20 nm (sometimes referred to as a“titanium oxide binder component” hereinafter) and a coating solutionfor forming a metal oxide semiconductor film for a photovoltaic cell,which comprises tubular titanium oxide particles and a dispersionmedium, are employed.

The peroxotitanic acid is prepared by adding hydrogen peroxide to anaqueous solution of a titanium compound or a sol or gel of hydratedtitanium oxide and heating the mixture.

The sol or gel of hydrated titanium oxide is obtained by adding an acidor an alkali to an aqueous solution of a titanium compound to performhydrolysis, and then if necessary, performing washing, heating andaging. The titanium compound used is not specifically restricted, but inparticular, titanium halides, titanium salts, such as titanyl sulfate,titanium alkoxides, such as tetraalkoxytitanium, and titanium compounds,such as titanium hydride, are preferably employable.

The titanium oxide particle dispersion sol is prepared by, for example,further heating the peroxotitanic acid and aging it.

The weight ratio (in terms of an oxide) of the titanium oxide bindercomponent to the tubular titanium oxide particles (titanium oxide bindercomponent/tubular titanium oxide particles) in the coating solution forforming a metal oxide semiconductor film for a photovoltaic cellemployable in the invention is desired to be in the range of 0.03 to0.50, preferably 0.1 to 0.3. If the weight ratio is less than the lowerlimit of the above range, visible light absorption is insufficient, andin some cases, the adsorption amount of the photosensitizer is notincreased. If the weight ratio is more than 0.50, a dense semiconductorfilm is not obtained occasionally, and besides the electron mobility isnot improved in some cases.

In the coating solution for forming a metal oxide semiconductor film fora photovoltaic cell, the titanium oxide binder component and the tubulartitanium oxide particles are desirably contained in a concentration of 1to 30% by weight, preferably 2 to 20% by weight, in terms of an oxide.

As the dispersion medium, any of dispersion media capable of dispersingtherein the titanium oxide binder component and the tubular titaniumoxide particles and capable of being removed when dried is employablewithout limitation. Particularly preferable are alcohols.

In the coating solution for forming a metal oxide semiconductor film fora photovoltaic cell employable in the invention, a film forming aid maybe contained, when needed. Examples of the film forming aids includepolyethylene glycol, polyvinyl pyrrolidone, hydroxypropyl cellulose,polyacrylic acid and polyvinyl alcohol. When the film forming aid iscontained in the coating solution, viscosity of the solution isincreased, and thereby it becomes possible to obtain a uniformly driedfilm. Moreover, the tubular titanium oxide particles are densely filledto increase bulk density, and a metal oxide semiconductor film havinghigh adhesion to the electrode can be obtained.

The process for producing a metal oxide semiconductor film for aphotovoltaic cell according to the invention comprises applying thecoating solution for forming a metal oxide semiconductor film for aphotovoltaic cell onto a substrate, drying the coating layer and thencuring the dried layer.

It is preferable to apply the coating solution in such a manner that thefilm thickness of the finally formed metal oxide semiconductor film isin the range of 0.1 to 50 μm. The coating solution can be applied by aconventional method, such as dipping, spinner method, spraying, rollcoating, flexographic printing or screen printing.

The drying temperature has only to be a temperature at which thedispersion medium can be removed.

In the present invention, it is particularly preferable to irradiate thecoating film with ultraviolet rays to cure the film. Although theirradiation dose of the ultraviolet rays varies depending upon thecontent of the peroxotitanic acid, etc., the film has only to beirradiated at a dose necessary to decompose and cure the peroxotitanicacid. When a film forming aid is contained in the coating solution, thefilm forming aid may be decomposed by heating after curing of thecoating film.

In the present invention, after the coating film is cured by irradiationwith ultraviolet rays, the film is preferably irradiated with ion of atleast one gas selected from O₂, N₂, and inert gases of Group 0 of theperiodic table, such as H₂, neon, argon and krypton, and then annealed.

For the ion irradiation, publicly known methods are adoptable. Forexample, a method of injecting boron or phosphorus into a silicon waferin a given amount and a given depth in the production of IC or LSI canbe adopted. Annealing is carried out by heating the film at atemperature of 200 to 500° C., preferably 250 to 400° C., for a periodof 10 minutes to 20 hours.

By virtue of the gas ion irradiation, no ion remains in the titaniumoxide film, and many defects are produced on the surfaces of titaniaparticles, whereby the crystalline state of the titanium oxide crystals(including brookite type crystals) after the annealing is improved, andbesides, bonding of particles is promoted. Consequently, the bindingpower to the photosensitizer is enhanced and the adsorption amount ofthe photosensitizer is increased. Further, by the promotion of particlebonding, the electron mobility is enhanced, and thereby photoelectricconversion efficiency can be enhanced.

The thickness of the metal oxide semiconductor film obtained above ispreferably in the range of 0.1 to 50 μm.

Photocatalyst

The photocatalyst according to the present invention uses the aforesaidtubular titanium oxide particles. For the photocatalyst, the tubulartitanium oxide particles can be used as they are, or they can be usedafter other active components are supported or doped thereon, or theycan be used after they are mixed with other active components. Thephotocatalyst may further contain a binder component precursor, ifnecessary.

There is no specific limitation on the usage form of the photocatalyst.For example, the tubular titanium oxide particles may be dispersed asthey are in a solvent such as water, or they may be mixed with a bindercomponent precursor to prepare a coating solution for forming aphotocatalyst layer, followed by application of the coating solutiononto a substrate, such as glass, PET, metal or ceramic, and drying toform a catalyst layer having a desired thickness. Further, the tubulartitanium oxide particles may be molded into spheres, pellets, honeycombsor the like.

Examples of the other active components include metal components usedfor the antibacterial or antifungal purpose, such as Ag, Cu and Zn, andmetal components having oxidation-reduction ability, such as Pt, Pd, Rh,Ru, Os, Ir, Au and Fe. For supporting or doping these metal components,hitherto known methods are adoptable. For example, an aqueous solutionof a metal component-soluble salt is added to a dispersion of thetubular titanium oxide particles, or if necessary, the resulting mixtureis hydrolyzed to precipitate the metal.

As the coating solution for forming a photocatalyst layer, the samesolution as the aforesaid coating solution for forming a metal oxidesemiconductor film is employable.

Examples of the binder component precursors employable in the inventioninclude inorganic metal salts or organic metal compounds, such assilicon tetrachloride, titanium tetrachloride, zirconium chloride, zincchloride, tin chloride, tetraethoxysilane, tetraisopropoxytitanium,tetraisopropoxyzirconium, tetraisopropoxyzinc, tetraisopropoxyindium andtetraisopropoxytin; partial hydrolyzates thereof; and hydrolysispolycondensates thereof.

As the tubular titanium oxide particles used for the photocatalyst ofthe invention, the aforesaid tubular titanium oxide particles used forthe photovoltaic cell are preferably employed.

The tubular titanium oxide particles desirably have an outer diameter(D_(out)) of 5 to 40 nm, preferably 10 to 30 nm, an inner diameter(D_(in)) of 4 to 30 nm, preferably 5 to 20 nm, a tube thickness of 1 to20 nm, preferably 2 to 15 nm, a length (L) of 25 to 1000 nm, preferably50 to 600 nm, and a length (L)/outer diameter (D_(out)) ratio(L/D_(out)) of 5 to 200, preferably 10 to 100. The tubular titaniumoxide having diameters, etc. of these ranges are particularly preferablefor a photocatalyst.

If the outer diameter (D_(out)) of the tubular titanium oxide particleis small, the inner diameter also becomes small correspondingly, so thatdiffusion of the reaction product becomes insufficient and satisfactoryactivity is not obtained occasionally, though it depends upon the typeof the reaction. Even if the outer diameter (D_(out)) of the tubulartitanium oxide particle is increased, light scattering takes place, sothat utilization of light is lowered and sufficient activity is notobtained occasionally.

If the inner diameter (D_(in)) of the tubular titanium oxide particle issmall, diffusion of the reaction product becomes insufficient andsatisfactory activity is not obtained occasionally, though it dependsupon the type of the reaction.

It is difficult to obtain tubular titanium oxide particles having aninner diameter (D_(in)) of large value, and even if they are obtained,the outer diameter (D_(out)) also becomes large correspondingly, andhence sufficient activity is not obtained occasionally because of lightscattering.

If the tube thickness is small, the thickness of the crystal layer alsobecomes small, and sufficient activity is not obtained occasionallybecause of insufficient production of electron holes.

Even if the tube thickness is increased, the feature that the specificsurface area is higher than that of conventional crystalline titaniumoxide becomes less distinct, so that the number of effective activesites, adsorption points of the reaction product, etc. is notsatisfactorily large, and the effect of increasing photocatalyticactivity sometimes becomes insufficient.

If the length (L) of the tubular titanium oxide particle is short,sufficient activity is not obtained occasionally in case ofrate-limiting reactions, though it depends upon the type of reaction. Ifthe length (L) of the tubular titanium oxide particle is too long,diffusion of the reaction product becomes insufficient and satisfactoryactivity is not obtained occasionally, though it depends upon the innerdiameter of the tube and the type of the reaction.

If the ratio of the length (L) of the tubular titanium oxide particle tothe outer diameter (D_(out)) thereof, i.e., (L)/(D_(out)) ratio, is lessthan the lower limit of the above range, adhesion of a catalyst film toa substrate or strength of the film sometimes becomes insufficient inthe case where the catalyst film is formed on the substrate.

If the (L)/(D_(out)) ratio is more than the upper limit of the aboverange, diffusion of the reaction product becomes insufficient andsatisfactory photocatalytic activity is not obtained occasionally,though it depends upon the type of the reaction.

The alkali metal content in the tubular titanium oxide particles ispreferably not more than 500 ppm, more preferably not more than 200 ppm,particularly preferably not more than 100 ppm.

If the alkali metal content is high, production of electron holes orelectron mobility is deteriorated, and sufficient photocatalyticactivity is not obtained occasionally.

Examples of catalytic reactions using the photocatalyst of the inventioninclude reduction of nitrogen oxide, reduction fixation of carbondioxide, decomposition of organic matters or environmental hormones inpolluted waste water, isomerization of olefins, photodecomposition ofwater, antifouling reaction, antifungal reaction, antibacterial reactionand deodorization reaction.

When the tubular titanium oxide particles are used for thephotocatalyst, a binder [B] composed of (b-1) titanium peroxide or (b-2)composite titanium peroxide, and (b-3) an organic high-molecular weightcompound may be used to form a film consisting of the tubular titaniumoxide particles [A] and the binder [B] on the substrate surface.

The titanium peroxide (b-1) is a compound usually represented byTiO₃.nH₂O. The titanium peroxide (b-1) can be obtained by reacting atitanium compound, such as a salt of titanium tetrachloride, titaniumhydroxide, titanium alkoxide or a titanium complex of acetylacetonato,with a peroxide, such as hydrogen peroxide.

The composite titanium peroxide (b-2) is a peroxide of composite metalscomposed of Ti and one or more elements selected from the groupconsisting of Cu, Ag, Zn, Cd, Al, Zr, Si, Sn, V, Nb, Sb, Bi, Cr, Mo, W,Mn and Fe (referred to as “element(s) (b)” hereinafter), and is acompound wherein a part of Ti atoms of the titanium peroxide (b-1) arereplaced with the elements (b) other than titanium.

The composite titanium peroxide (b-2) can be obtained by reacting theaforesaid titanium compound with a compound, such as a salt, hydroxide,alkoxide or acetylacetonato complex of an element other than titanium,and a peroxide, such as hydrogen peroxide. For example, hydrogenperoxide is added to a water/alcohol solution of isopropoxytitanium andisopropoxyzirconium, and the mixture is subjected to heat treatment,whereby a composite peroxide of titanium and zirconium is obtained. Thetitanium peroxide (b-1) or the composite titanium peroxide (b-2) isusually in the state of a solution.

Since the titanium peroxide (b-1) or the composite titanium peroxide(b-2) has a refractive index almost the same as that of the aforesaidtubular titanium oxide particles, light scattering due to the filmforming components is decreased, and a film of excellent transparencycan be formed.

Especially when a composite peroxide of Ti and Zr and/or Si is used asthe titanium peroxide or the composite titanium peroxide, adhesion tothe substrate and affinity for the organic solvent are greatly improved,so that use of the composite peroxide is preferable.

The titanium peroxide or the composite titanium peroxide may be reactedwith organic amine or acetylacetone prior to use. When a transparentcoating film is formed by the use of a coating solution containing theabove peroxide as a binder, the peroxide is decomposed in the heattreatment of the film forming process, and thereby densification of thefilm can be accelerated. When the titanium peroxide or the compositetitanium peroxide is contained as a binder, the binder itself comes tohave photocatalytic activity and conductivity. Therefore, thephotocatalytic activation is promoted to thereby enhance photocatalyticactivity of the resulting film. Further, because the refractive index ofthe binder is almost the same as that of the composite titanium oxidefine particles, it is possible to form a coating film having hightransparency and low haze. Moreover, even if the film is treated at alow temperature of about 150° C., hardening of the film is feasible.Hence, a film having excellent adhesion to a substrate of glass, plasticor the like can be formed, and besides a film having a thickness ofabout 1 μm can be easily formed by one coating.

The organic high-molecular weight compound (b-3) contained in the binderis preferably polysaccharide such as chitosan or cellulose. When theorganic high-molecular weight compound (b-3) is contained in the binder,stress accompanying shrinkage of the coating film in the drying step ofthe film forming process is relaxed to prevent cracking of the film, andhence it becomes possible to increase the film thickness. Moreover,wettability of the substrate by the coating solution is increased, andviscosity of the coating solution is also increased. Hence, workabilityof the coating process can be improved.

In order to form a coating film on the substrate surface to prepare aphotocatalyst, the tubular titanium oxide fine particles [A] and thebinder [B] are dissolved or dispersed in a solvent consisting of waterand/or an organic solvent to prepare a coating solution for forming atransparent coating film. Then, the coating solution is applied onto asurface of a substrate, such as glass, plastic, ceramic or fiber, by ausual method, such as spinner method, bar coating, spraying, dipping orflexographic method, then dried and cured under heating at 150 to 400°C. For the curing treatment, ultraviolet irradiation may be used incombination. The thickness of the transparent coating film is desired tobe in the range of about 0.1 to 10 μm, preferably 0.2 to 5 μm.

The tubular titanium oxide particles used in the present invention havesuch constitutions as previously described and have a high specificsurface area of 200 to 600 m²/g, so that large amounts of sensormolecules can be adsorbed. Therefore, these particles can be favorablyused as detective parts of an optical sensor even if extremely weaklight is used.

Further, because the tubular titanium oxide particles have the aforesaid(L)/(D_(out)) ratio and tube thickness, the light transmission of theparticles is excellent, and moving of electron holes in the particlerapidly takes place, differently from the case of using extremely finetitanium oxide particles. Therefore, an optical sensor having highdetection accuracy can be obtained.

Furthermore, because the tubular titanium oxide particles have theaforesaid constitutions, they are useful as negative pole materials ofbatteries by introducing Li into them.

According to the present invention, a water dispersion sol of titaniumoxide particles and/or titanium oxide type composite oxide particlescomprising titanium oxide and/or an oxide other than titanium oxide,said particles functioning titanium oxide source and having specificparticle diameter, is used. Therefore, it is unnecessary to calcine thetitanium oxide source at a high temperature to crystallize it, andtubular titanium oxide containing small amounts of agglomerates andhaving uniform particle shape and a low content of residual alkali metalcan be obtained in a high yield. Accordingly, a process for preparingtubular titanium oxide particles which are useful as starting substancesof functional materials, such as catalysts, catalyst carriers,photocatalysts, decorative materials, optical materials andphotoelectric conversion materials, and such tubular titanium oxideparticles can be provided. The reduction type tubular titanium oxideparticles are useful as catalysts, adsorbents, photocatalysts, opticalmaterials, photoelectric conversion materials, etc., and besides, theyare effectively used for proton conductive materials, electrolyte filmsfor fuel cells and other conductive materials because they haveconductivity.

According to the present invention, the above-mentioned tubular titaniumoxide particles are used for a metal oxide semiconductor film.Therefore, the adsorption amount of a photosensitizer on the metal oxidesemiconductor film is large, diffusion of the electrolyte is excellent,and the content of alkali metal is extremely low. Hence, a photovoltaiccell improved in the photoelectric conversion efficiency and useful forvarious photoelectric conversion systems can be obtained. Further, aphotocatalyst having an extremely low content of alkali metal,exhibiting excellent diffusion of reaction products or other productsand having high activity can be obtained. The tubular titanium oxideparticles are useful not only as photovoltaic cells and photocatalystsbut also as negative pole materials of batteries and detective parts ofoptical sensors.

EXAMPLES

The present invention is further described with reference to thefollowing examples, but it should be construed that the invention is inno way limited to those examples.

Example A1 Preparation of Titanium Oxide Particle (T-1) Dispersion

A titanium chloride aqueous solution was diluted with pure water toprepare a titanium chloride aqueous solution having a concentration (interms of TiO₂, referred to as “TiO₂ concentration” hereinafter) of 5% byweight. The aqueous solution was added to ammonia water having aconcentration of 15% by weight and having been controlled to atemperature of 5° C. to perform neutralization and hydrolysis. After theaddition of the titanium chloride aqueous solution, the resulting gelhad pH of 10.5. Then, the gel was washed by filtration to obtain a gelof orthotitanic acid having a TiO₂ concentration of 9% by weight.

Thereafter, 100 g of the gel of orthotitanic acid was dispersed in 2900g of pure water, then 800 g of hydrogen peroxide water having aconcentration of 35% by weight was added, and with stirring, the mixturewas heated at 85° C. for 3 hours to prepare a peroxotitanic acid aqueoussolution. The peroxotitanic acid aqueous solution obtained had a TiO₂concentration of 0.5% by weight. As the dispersion medium, water wasused.

Subsequently, the resulting solution was heated at 95° C. for 10 hoursto give a titanium oxide particle dispersion, and to the titanium oxideparticle dispersion, tetramethylammonium hydroxide (TMAH, MW: 149.2) wasadded in such an amount that the molar ratio of TMAH to TiO₂ in thedispersion became 0.016. The resulting dispersion had pH of 11. Then,the dispersion was subjected to hydrothermal treatment at 230° C. for 5hours to prepare a titanium oxide particle (T-1) dispersion. An averageparticle diameter of the titanium oxide particles (T-1) is set forth inTable 1.

Preparation of Tubular Titanium Oxide Particles (PT-1-1)

To the titanium oxide particle (T-1) dispersion, 70 g of a NaOH aqueoussolution having a concentration of 40% by weight was added in such amanner that the molar ratio (A_(M))/(T_(M)) of the number of moles(A_(M)) of the alkali metal hydroxide to the number of moles (T_(M)) ofTiO₂ became 10, and the mixture was subjected to hydrothermal treatmentat 150° C. for 2 hours.

The resulting particles were sufficiently washed with pure water. Theamount of residual Na₂O was 0.9% by weight. Then, alkali was decreasedby the use of a cation exchange resin to prepare tubular titanium oxideparticles (PT-1-1). The amount of residual Na₂O in the resultingparticles (PT-1-1) was analyzed. Further, the crystalline state of theparticles was measured by X-ray diffractometry and evaluated based onthe following criteria.

The results are set forth in Table 1. The crystal type (crystal form) ofthe resulting particles (PT-1-1) was anatase type.

Criteria

Evaluation was made based on the height of a peak at a lattice constantd of 1.89.

AA: The peak is obviously higher than that of the tubular titanium oxideparticles (PT1-1).

BB: The peak is almost the same as that of the tubular titanium oxideparticles (PT1-1).

CC: The peak is obviously lower than that of the tubular titanium oxideparticles (PT1-1).

DD: The particles are substantially amorphous.

Example A2 Preparation of Tubular Titanium Oxide Particles (PT-1-2)

To a water dispersion (TiO₂ concentration: 5% by weight) of the tubulartitanium oxide particles (PT) obtained in Example A1,tetramethylammonium hydroxide was added as an organic base in such anamount that the molar ratio of TMAH to TiO₂ became 0.1. The resultingdispersion had pH of 13.2. Then, the dispersion was subjected tohydrothermal treatment at 190° C. for 5 hours to prepare tubulartitanium oxide particles (PT-1-2). The resulting tubular titanium oxideparticles (PT-1-2) were washed with water and dried. Then, alkali wasanalyzed, and a TEM photograph of the particles was taken to determinean average particle length (L), an average tube outer diameter (D_(out))and an average tube inner diameter (D_(in)). Further, specific surfacearea of the particles and the crystalline state thereof were evaluated.The results are set forth in Table 1.

Example A3 Preparation of Tubular Titanium Oxide Particles (PT-2-1)

To a titanium oxide particle (T-1) dispersion prepared in the samemanner as in Example A1, 40 g of a NaOH aqueous solution having aconcentration of 40% by weight and 358 g of a tetramethylammoniumhydroxide (TMAH) aqueous solution having a concentration of 25% byweight were added in such a manner that the molar ratio[(A_(M))+(OB_(M))]/(T_(M)) of the total of the number of moles (A_(M))of the alkali metal hydroxide and the number of moles (OB_(M)) of theorganic base to the number of moles (T_(M)) of TiO₂ became 10, and themixture was subjected to hydrothermal treatment at 150° C. for 2 hours.The resulting particles were sufficiently washed with pure water. Theamount of residual Na₂O was 0.3% by weight. Then, alkali was decreasedby the use of a cation exchange resin to prepare tubular titanium oxideparticles (PT-2-1). The amount of residual Na₂O in the resultingparticles (PT-2-1) was analyzed, and the crystalline state of theparticles was measured by X-ray diffractometry.

The results are set forth in Table 1.

Example A4 Preparation of Tubular Titanium Oxide Particles (PT-2-2)

To a water dispersion (TiO₂ concentration: 5% by weight) of the tubulartitanium oxide particles (PT-2-1) obtained in Example A3,tetramethylammonium hydroxide (TMAH) was added as an organic base insuch an amount that the molar ratio of TMAH to TiO₂ became 0.1. Theresulting dispersion had pH of 13.0. Then, the dispersion was subjectedto hydrothermal treatment at 230° C. for 5 hours to prepare tubulartitanium oxide particles (PT-2-2).

The resulting tubular titanium oxide particles (PT-2-2) were washed withwater and dried. Then, alkali was analyzed, and a TEM photograph of theparticles was taken to determine an average particle length (L), anaverage tube outer diameter (D_(out)) and an average tube inner diameter(D_(in)). Further, specific surface area of the particles and thecrystalline state thereof were evaluated.

The results are set forth in Table 1.

Example A5 Preparation of Titanium Oxide Type Composite Oxide Particle(T-3) Dispersion

A peroxotitanic acid aqueous solution (TiO₂ concentration: 0.5% byweight) of 3800 g was prepared in the same manner as in Example A1. Theaqueous solution was mixed with 7.0 g of a silica sol (available fromCatalysts & Chemicals Industries Co., Ltd., SI-350, SiO₂ concentration:30% by weight, average particle diameter: 8 nm), and the mixture washeated at 95° C. for 3 hours to prepare a titanium oxide type compositeoxide particle (T-3) dispersion having a TiO₂.SiO₂ concentration of0.56% by weight. An average particle diameter of the oxide particles(T-3) is set forth in Table 1.

Preparation of Tubular Titanium Oxide Particles (PT-3-1)

To the titanium oxide type composite oxide particle (T-3) dispersion, 70g of a NaOH aqueous solution having a concentration of 40% by weight wasadded in such a manner that the molar ratio (A_(M))/(T_(M)) of thenumber of moles (A_(M)) of the alkali metal hydroxide to the number ofmoles (T_(M)) of TiO₂ became 10, and the mixture was subjected tohydrothermal treatment at 150° C. for 2 hours. The resulting particleswere sufficiently washed with pure water. The amount of residual Na₂Owas 1.5% by weight.

Then, alkali was decreased by the use of a cation exchange resin toprepare tubular titanium oxide particles (PT-3-1). The amount ofresidual Na₂O in the resulting particles (PT-3-1) was analyzed, and thecrystalline state of the particles was measured by X-ray diffractometry.

The results are set forth in Table 1.

Example A6 Preparation of Tubular Titanium Oxide Particles (PT-3-2)

To a water dispersion (TiO₂.SiO₂ concentration: 3% by weight) of thetubular titanium oxide particles (PT-3-1) obtained in Example A5,tetramethylammonium hydroxide (TMAH) was added as an organic base insuch an amount that the molar ratio of TMAH to TiO₂ became 0.1. Theresulting dispersion had pH of 13.0. Then, the dispersion was subjectedto hydrothermal treatment at 230° C. for 5 hours to prepare tubulartitanium oxide particles (PT-3-2).

The resulting tubular titanium oxide particles (PT-3-2) were washed withwater and dried. Then, alkali and SiO₂ were analyzed, and a TEMphotograph of the particles was taken to determine an average particlelength (L), an average tube outer diameter (D_(out)) and an average tubeinner diameter (D_(in)). Further, specific surface area of the particlesand the crystalline state thereof were evaluated.

The results are set forth in Table 1.

Example A7 Preparation of Titanium Oxide Type Composite Oxide Particle(T-4) Dispersion

A peroxotitanic acid aqueous solution (TiO₂ concentration: 0.5% byweight) of 3800 g was prepared in the same manner as in Example A1. Theaqueous solution was mixed with 15.8 g of a silica sol (available fromCatalysts & Chemicals Industries Co., Ltd., SI-550, SiO₂ concentration:30% by weight, average particle diameter: 8 nm), and the mixture washeated at 95° C. for 3 hours to prepare a titanium oxide type compositeoxide particle (T-4) dispersion having a TiO₂.SiO₂ concentration of0.62% by weight. An average particle diameter of the oxide particles(T-4) is set forth in Table 1.

Preparation of Tubular Titanium Oxide Particles (PT-4-1)

To the titanium oxide type composite oxide particle (T-4) dispersion, 70g of a NaOH aqueous solution having a concentration of 40% by weight wasadded in such a manner that the molar ratio (A_(M))/(T_(M)) of thenumber of moles (A_(M)) of the alkali metal hydroxide to the number ofmoles (T_(M)) of TiO₂ became 10, and the mixture was subjected tohydrothermal treatment at 150° C. for 2 hours. The resulting particleswere sufficiently washed with pure water. The amount of residual Na₂Owas 2.0% by weight. Then, alkali was decreased by the use of a cationexchange resin to prepare tubular titanium oxide particles (PT-4-1). Theamount of residual Na₂O in the resulting particles (PT-4-1) wasanalyzed, and the crystalline state of the particles was measured byX-ray diffractometry.

The results are set forth in Table 1.

Example A8 Preparation of Tubular Titanium Oxide Particles (PT-4-2)

To a water dispersion (TiO₂.SiO₂ concentration: 3% by weight) of thetubular titanium oxide particles (PT-4-1) obtained in Example A7,tetramethylammonium hydroxide (TMAH) was added as an organic base insuch an amount that the molar ratio of TMAH to TiO₂ became 0.1. Theresulting dispersion had pH of 13.5. Then, the dispersion was subjectedto hydrothermal treatment at 230° C. for 5 hours to prepare tubulartitanium oxide particles (PT-4-2).

The resulting tubular titanium oxide particles (PT-4-2) were washed withwater and dried. Then, alkali and SiO₂ were analyzed, and a TEMphotograph of the particles was taken to determine an average particlelength (L), an average tube outer diameter (D_(out)) and an average tubeinner diameter (D_(in)). Further, specific surface area of the particlesand the crystalline state thereof were evaluated.

The results are set forth in Table 1.

Example A9 Preparation of Titanium Oxide Type Composite Oxide Particle(T-5) Dispersion

A peroxotitanic acid aqueous solution (TiO₂ concentration: 0.5% byweight) of 3800 g was prepared in the same manner as in Example A1. Theaqueous solution was mixed with 21 g of an alumina sol (available fromCatalysts & Chemicals Industries Co., Ltd., AS-2, Al₂O₃ concentration:10% by weight); and the mixture was heated at 95° C. for 3 hours toprepare a titanium oxide type composite oxide particle (T-5) dispersionhaving a TiO₂.Al₂O₃ concentration of 0.55% by weight. An averageparticle diameter of the oxide particles (T-5) is set forth in Table 1.

Preparation of Tubular Titanium Oxide Particles (PT-5-1)

To the titanium oxide type composite oxide particle (T-5) dispersion, 70g of a NaOH aqueous solution having a concentration of 40% by weight wasadded in such a manner that the molar ratio (A_(M))/(T_(M)) of thenumber of moles (A_(M)) of the alkali metal hydroxide to the number ofmoles (T_(M)) of TiO₂ became 10, and the mixture was subjected tohydrothermal treatment at 150° C. for 2 hours. The resulting particleswere sufficiently washed with pure water. The amount of residual Na₂Owas 1.6% by weight. Then, alkali was decreased by the use of a cationexchange resin to prepare tubular titanium oxide particles (PT-5-1). Theamount of residual Na₂O in the resulting particles (PT-5-1) wasanalyzed, and the crystalline state of the particles was measured byX-ray diffractometry.

The results are set forth in Table 1.

Example A10 Preparation of Tubular Titanium Oxide Particles (PT-5-2)

To a water dispersion (TiO₂.Al₂O₃ concentration: 3% by weight) of thetubular titanium oxide particles (PT-5-1) obtained in Example A9,tetramethylammonium hydroxide (TMAH) was added as an organic base insuch an amount that the molar ratio of TMAH to TiO₂ became 0.1. Theresulting dispersion had pH of 13.2. Then, the dispersion was subjectedto hydrothermal treatment at 230° C. for 5 hours to prepare tubulartitanium oxide particles (PT-5-2).

The resulting tubular titanium oxide particles (PT-5-2) were washed withwater and dried. Then, alkali and Al₂O₃ were analyzed, and a TEMphotograph of the particles was taken to determine an average particlelength (L), an average tube outer diameter (D_(out)) and an average tubeinner diameter (D_(in)). Further, specific surface area of the particlesand the crystalline state thereof were evaluated.

The results are set forth in Table 1.

Example A11 Preparation of Titanium Oxide Type Composite Oxide Particle(T-6) Dispersion

A peroxotitanic acid aqueous solution (TiO₂ concentration: 0.5% byweight) of 3800 g was prepared in the same manner as in Example A1. Theaqueous solution was mixed with 19 g of a zirconia sol prepared in thefollowing manner, and the mixture was heated at 95° C. for 3 hours toprepare a titanium oxide type composite oxide particle (T-6) dispersionhaving a TiO₂.ZrO₂ concentration of 0.52% by weight. An average particlediameter of the oxide particles (T-6) is set forth in Table 1.

Preparation of Zirconia Sol

In a flask equipped with a dry distillation device, 5 kg of a zirconiumchloride aqueous solution containing 0.036% by weight of zirconiumchloride was placed, and with sufficient stirring, 290 g of 0.1 Nammonia water was slowly added. The resulting solution was heated at 95°C. for 50 hours to obtain an opaque white sol having a ZrO₂concentration of 0.034% by weight and pH of 1.8. Then, 0.1 N ammoniawater was further added to adjust pH to 4.8, and the resulting solutionwas washed with ion exchange water until no chlorine ion was detected inthe filtrate to prepare a zirconia sol (average particle diameter: 50nm) having a ZrO₂ concentration of 5% by weight as a dispersion.

Preparation of Tubular Titanium Oxide Particles (PT-6-1)

To the titanium oxide particle (T-6) dispersion, 70 g of a NaOH aqueoussolution having a concentration of 40% by weight was added in such amanner that the molar ratio (A_(M))/(T_(M)) of the number of moles(A_(M)) of the alkali metal hydroxide to the number of moles (T_(M)) ofTiO₂ became 10, and the mixture was subjected to hydrothermal treatmentat 150° C. for 2 hours. The resulting particles were sufficiently washedwith pure water. The amount of residual Na₂O was 1.7% by weight. Then,alkali was decreased by the use of a cation exchange resin to preparetubular titanium oxide particles (PT-6-1). The amount of residual Na₂Oin the resulting particles (PT-6-1) was analyzed, and the crystallinestate of the particles was measured by X-ray diffractometry.

The results are set forth in Table 1.

Example A12 Preparation of Tubular Titanium Oxide Particles (PT-6-2)

To a water dispersion (TiO₂.ZrO₂ concentration: 3% by weight) of thetubular titanium oxide particles (PT-6-1) obtained in Example A11,tetramethylammonium hydroxide (TMAH) was added as an organic base insuch an amount that the molar ratio of TMAH to TiO₂ became 0.1. Theresulting dispersion had pH of 13.5. Then, the dispersion was subjectedto hydrothermal treatment at 230° C. for 5 hours to prepare tubulartitanium oxide particles (PT-6-2).

The resulting tubular titanium oxide particles (PT-6-2) were washed withwater and dried. Then, alkali and ZrO₂ were analyzed, and a TEMphotograph of the particles was taken to determine an average particlelength (L), an average tube outer diameter (D_(out)) and an average tubeinner diameter (D_(in)). Further, specific surface area of the particlesand the crystalline state thereof were evaluated.

The results are set forth in Table 1.

Example A13 Preparation of Tubular Titanium Oxide Particles (PT-1-2)

To a water dispersion (TiO₂ concentration: 5% by weight) of the tubulartitanium oxide particles (PT-1-1) obtained in Example A1, citric acidwas added as an organic base in such an amount that the molar ratio ofcitric acid to TiO₂ became 3.0. The resulting dispersion had pH of 3.0.Then, the dispersion was subjected to hydrothermal treatment at 190° C.for 5 hours to prepare tubular titanium oxide particles (PT-1-13).

The resulting tubular titanium oxide particles (PT-1-13) were washedwith water and dried. Then, alkali was analyzed, and a TEM photograph ofthe particles was taken to determine an average particle length (L), anaverage tube outer diameter (D_(out)) and an average tube inner diameter(D_(in)). Further, specific surface area of the particles and thecrystalline state thereof were evaluated.

The results are set forth in Table 1.

Comparative Example A1 Preparation of Titanium Oxide Particle (T-7)Dispersion

A titanium oxide particle (T-1) dispersion prepared in the same manneras in Example A1 was dried and then calcined at 600° C. for 2 hours. Thecalcined product was pulverized to obtain a titanium oxide powder havingan average particle diameter of 200 nm. Then, the powder was dispersedin water to prepare a titanium oxide particle (T-7) dispersion having aTiO₂ concentration of 10% by weight.

Preparation of Tubular Titanium Oxide Particles (PT-7-1)

To the titanium oxide particle (T-7) dispersion, 70 g of a NaOH aqueoussolution having a concentration of 40% by weight was added in such amanner that the molar ratio (A_(M))/(T_(M)) of the number of moles(A_(M)) of the alkali metal hydroxide to the number of moles (T_(M)) ofTiO₂ became 10, and the mixture was subjected to hydrothermal treatmentat 150° C. for 2 hours. The resulting particles were sufficiently washedwith pure water. The amount of residual Na₂O was 2.5% by weight. Then,alkali was decreased by the use of a cation exchange resin to preparetubular titanium oxide particles (PT-7-1). The amount of residual Na₂Oin the resulting particles (PT-7-1) was analyzed, and the crystallinestate of the particles was measured by X-ray diffractometry.

The results are set forth in Table 1.

Comparative Example A2 Preparation of Tubular Titanium Oxide Particles(PT-7-2)

To a water dispersion (TiO₂ concentration: 3% by weight) of the tubulartitanium oxide particles (PT-7-1) obtained in Example A1,tetramethylammonium hydroxide (TMAH) was added as an organic base insuch an amount that the molar ratio of TMAH to TiO₂ became 0.1. Theresulting dispersion had pH of 13.2. Then, the dispersion was subjectedto hydrothermal treatment at 230° C. for 5 hours to prepare tubulartitanium oxide particles (PT-7-2).

The resulting tubular titanium oxide particles (PT-7-2) were washed withwater and dried. Then, alkali was analyzed, and a TEM photograph of theparticles was taken to determine an average particle length (L), anaverage tube outer diameter (D_(out)) and an average tube inner diameter(D_(in)). Further, specific surface area of the particles and thecrystalline state thereof were evaluated.

The results are set forth in Table 1.

Comparative Example A3 Preparation of Titanium Oxide Type CompositeOxide Particle (T-8) Dispersion

A titanium oxide type composite oxide particle (T-8) dispersion preparedin the same manner as in Example A5 was dried and then calcined at 600°C. for 2 hours. The calcined product was pulverized to obtain a titaniumoxide powder having an average particle diameter of 300 nm. Then, thepowder was dispersed in water to prepare a titanium oxide type compositeoxide particle (T-8) dispersion having a TiO₂.SiO₂ concentration of 10%by weight.

Preparation of Tubular Titanium Oxide Particles (PT-8-1)

To the titanium oxide type composite oxide particle (T-8) dispersion, 70g of a NaOH aqueous solution having a concentration of 40% by weight wasadded in such a manner that the molar ratio (A_(M))/(T_(M)) of thenumber of moles (A_(M)) of the alkali metal hydroxide to the number ofmoles (T_(M)) of TiO₂ became 10, and the mixture was subjected tohydrothermal treatment at 150° C. for 2 hours. The resulting particleswere sufficiently washed with pure water. The amount of residual Na₂Owas 5.0% by weight. Then, alkali was decreased by the use of a cationexchange resin to prepare tubular titanium oxide particles (PT-8-1). Theamount of residual Na₂O in the resulting particles (PT-8-1) wasanalyzed.

The results are set forth in Table 1.

Comparative Example A4 Preparation of Tubular Titanium Oxide Particles(PT-8-2)

To a water dispersion (TiO₂ concentration: 3% by weight) of the tubulartitanium oxide particles (PT-8-1) obtained in Comparative Example A3,tetramethylammonium hydroxide (TMAH) was added as an organic base insuch an amount that the molar ratio of TMAH to TiO₂ became 0.1. Theresulting dispersion had pH of 13.2. Then, the dispersion was subjectedto hydrothermal treatment at 230° C. for 5 hours to prepare tubulartitanium oxide particles (PT-8-2).

The resulting tubular titanium oxide particles (PT-8-2) were washed withwater and dried. Then, alkali and SiO₂ were analyzed, and a TEMphotograph of the particles was taken to determine an average particlelength (L), an average tube outer diameter (D_(out)) and an average tubeinner diameter (D_(in)). Further, specific surface area of the particlesand the crystalline state thereof were evaluated.

The results are set forth in Table 1.

TABLE 1 Titanium oxide type particle dispersion First hydrothermaltreatment Average Solids Type A_(H)/T_(H) Temper- Na₂O after IE resinType of Composi- particle concentration of molar ature Time waterwashing¹⁾ Na₂O²⁾ oxide tion diameter (nm) (wt. %) alkali ratio pH (° C.)(hr) (wt. %) (wt. %) Ex. A1 TiO₂ 100 30 0.5 NaOH 10 14 or 150 2 0.9 0.15more Ex. A2 TiO₂ 100 30 0.5 NaOH 10 14 or 150 2 0.9 0.15 more Ex. A3TiO₂ 100 30 0.5 NaO 10 14 or 150 2 0.3 0.12 TMAH more Ex. A4 TiO₂ 100 300.5 NaO 10 14 or 150 2 0.3 0.12 TMAH more Ex. A5 TiO₂•SiO₂ 90/10 20 0.5NaOH 10 14 or 150 2 1.5 0.45 more Ex. A6 TiO₂•SiO₂ 90/10 20 0.5 NaOH 1014 or 150 2 1.5 0.45 more Ex. A7 TiO₂•SiO₂ 80/20 10 0.5 NaOH 10 14 or150 2 2.0 0.50 more Ex. A8 TiO₂•SiO₂ 80/20 10 0.5 NaOH 10 14 or 150 22.0 0.50 more Ex. A9 TiO₂•Al₂O₃ 90/10 20 0.5 NaOH 10 14 or 150 2 1.60.50 more Ex. A10 TiO₂•Al₂O₃ 90/10 20 0.5 NaOH 10 14 or 150 2 1.6 0.50more Ex. A11 TiO₂•ZrO₂ 95/5 10 0.5 NaOH 10 14 or 150 2 1.7 0.30 more Ex.A12 TiO₂•ZrO₂ 95/5 10 0.5 NaOH 10 14 or 150 2 1.7 0.30 more Ex. A13 TiO₂100 30 0.5 NaOH 10 14 or 150 2 0.9 0.15 more Comp. Ex. A1 TiO₂ 100 20010 NaOH 10 14 or 150 2 2.5 0.60 more Comp. Ex. A2 TiO₂ 100 200 10 NaOH10 14 or 150 2 2.5 0.60 more Comp. Ex. A3 TiO₂•SiO₂ 85/15 300 10 NaOH 1014 or 150 2 5.0 0.70 more Comp. Ex. A4 TiO₂•SiO₂ 85/15 300 10 NaOH 10 14or 150 2 5.0 0.70 more Second hydrothermal treatment Tubular titaniumoxide particles Na₂O Average after water particle Average AverageSpecific Type Temperature Time washing¹⁾ length tube outer tube innersurface area Mo_(x) ³⁾ of base pH (° C.) (hr) (ppm) (nm) diameter (nm)diameter (nm) Crystalline state (m²/g) (wt. %) Ex. A1 180 10 7.5 anatase—⁴⁾ 450 — Ex. A2 TMAH 13.2 190 5 50 180 10 7.5 anatase AA 450 — Ex. A3175 10 7.5 anatase BB 450 — Ex. A4 TMAH 13.0 230 5 10 175 10 7.5 anataseAA 400 — Ex. A5 145 10 7.5 anatase BB 400 3 Ex. A6 TMAH 13.0 230 5 100145 10 7.5 anatase AA 500 3 Ex. A7 225 10 7.5 anatase BB 500 6 Ex. A8TMAH 13.5 230 5 200 225 10 7.5 anatase AA 450 6 Ex. A9 175 10 7.5anatase BB 450 3 Ex. A10 TMAH 13.2 230 5 200 175 10 7.5 anatase AA 450 3Ex. A11 175 10 7.5 anatase BB 450 4 Ex. A12 TMAH 13.5 230 5 100 175 107.5 anatase AA 500 4 Ex. A13 citric 3.0 190 5 30 180 10 7.5 anatase AA450 — acid Comp. 375 10 7.5 anatase + Am CC 450 — Ex. A1 Comp. TMAH 13.2230 5 1100 375 10 7.5 anatase + Am CC 450 — Ex. A2 Comp. 375 10 7.5anatase + Am CC 500 — Ex. A3 Comp. TMAH 13.2 230 5 1600 375 10 7.5anatase + Am CC 500 — Ex. A4 Notes: In A_(H), an organic base O_(H) isincluded. ¹⁾NaO₂ after water washing means an amount (in terms of oxide)of sodium in the particles obtained by washing with water afterhydrothermal treatment. ²⁾IE resin NaO₂ means an amount (in terms ofoxide) of sodium in the particles obtained by conducting ion exchangeresin treatment after washing with water. ³⁾Mo_(x) means a content of ametal oxide other than titanium oxide. ⁴⁾The crystal state was notevaluated because it was used as a criterion.

Example B1 Preparation of Titanium Oxide Particle (T-1) Dispersion

A titanium chloride aqueous solution was diluted with pure water toprepare a titanium chloride aqueous solution having a TiO₂ concentrationof 5% by weight. The aqueous solution was added to ammonia water havinga concentration of 15% by weight and having been controlled to atemperature of 5° C. to perform neutralization and hydrolysis. After theaddition of the titanium chloride aqueous solution, the resulting gelhad pH of 10.5. Then, the gel was washed by filtration to obtain a gelof orthotitanic acid having a TiO₂ concentration of 9% by weight.

Thereafter, 100 g of the gel of orthotitanic acid was dispersed in 2900g of pure water, then 800 g of hydrogen peroxide water having aconcentration of 35% by weight was added, and with stirring, the mixturewas heated at 85° C. for 3 hours to prepare a peroxotitanic acid aqueoussolution. The peroxotitanic acid aqueous solution obtained had a TiO₂concentration of 0.5% by weight.

Subsequently, the resulting solution was heated at 95° C. for 10 hoursto give a titanium oxide particle dispersion, and to the titanium oxideparticle dispersion, tetramethylammonium hydroxide (TMAH, MW: 149.2) wasadded in such an amount that the molar ratio of TMAH to TiO₂ in thedispersion became 0.016. The resulting dispersion had pH of 11. Then,the dispersion was subjected to hydrothermal treatment at 230° C. for 5hours to prepare a titanium oxide particle (T-1) dispersion. An averageparticle diameter of the titanium oxide particles (T-1) is set forth inTable 2.

Preparation of Reduction Type Tubular Titanium Oxide Particles (RPT-1)

To the titanium oxide particle (T-1) dispersion, 70 g of a KOH aqueoussolution having a concentration of 40% by weight was added in such amanner that the molar ratio (A_(M))/(T_(M)) of the number of moles(A_(M)) of the alkali metal hydroxide to the number of moles (T_(M)) ofTiO₂ became 10, and the mixture was subjected to hydrothermal treatmentat 150° C. for 2 hours (first hydrothermal treatment).

The resulting particles were sufficiently washed with pure water. Theamount of residual K₂O was 0.9% by weight. After washing with purewater, a water dispersion (TiO₂ concentration: 5% by weight) of thetubular titanium oxide particles was prepared. To the water dispersion,a cation exchange resin and an anion exchange resin were added in thesame amount as that of the tubular titanium oxide particles, and themixture was treated at 60° C. for 24 hours to perform high purificationsuch as removal of alkali.

Then, freeze drying was carried out to obtain tubular titanium oxideparticles (PT-1).

The tubular titanium oxide particles (PT-1) were placed in an electricoven having been controlled to 400° C., and an ammonia gas (NH₃, 10% byvolume) diluted with nitrogen was fed to the electric oven for 2 hoursto prepare reduction type tubular titanium oxide particles (RPT-1).

The composition parameters of the resulting reduction type tubulartitanium oxide particles (RPT-1) and the amount of residual K₂O weremeasured. The results are set forth in Table 2. Further, a TEMphotograph of the particles was taken to determine an average particlelength (L), an average tube outer diameter (D_(out)) and an average tubeinner diameter (D_(in)). The results are set forth in Table 2.

Furthermore, a powder resistance value was measured as electricalconductivity. The result is set forth in Table 2.

The powder resistance value was measured in the following manner. Into athrough type alumina cylinder (inner sectional area: 1 cm²), aconductive columnar electrode of piston type was first inserted at thebottom, then about 5 g of the reduction type tubular titanium oxideparticles (RPT-1) were filled, and thereafter a conductive columnarelectrode of piston type was also inserted at the top. Then, a pressureof 100 kg/cm² was applied to the powder by means of a hydraulic press,and in this state, terminals of a digital multimeter (tester) wereconnected to the upper and the lower columnar electrodes to measure aresistance value. The measured value was divided by a height of thepressurized powder filled. The result is set forth in Table 2.

Example B2 Preparation of Reduction Type Tubular Titanium OxideParticles (RPT-2)

A water dispersion (TiO₂ concentration: 5% by weight) of the tubulartitanium oxide particles obtained by the washing with water after thefirst hydrothermal treatment in Example B1 was prepared in an amount of140 g. To the water dispersion, 0.35 g of citric acid was added, andthen the mixture was subjected to hydrothermal treatment at 60° C. for24 hours (second hydrothermal treatment). Then, washing with water andfreeze drying were carried out to prepare tubular titanium oxideparticles (PT-2).

Subsequently, the tubular titanium oxide particles were subjected toreduction treatment in the same manner as in Example B1 to preparereduction type tubular titanium oxide particles (RPT-2).

The composition parameters of the resulting reduction type tubulartitanium oxide particles (RPT-2) and the amount of residual K₂O weremeasured. The results are set forth in Table 2. Further, a TEMphotograph of the particles was taken to determine an average particlelength (L), an average tube outer diameter (D_(out)) and an average tubeinner diameter (D_(in)). Furthermore, electrical conductivity wasmeasured. The results are set forth in Table 2.

Example B3 Preparation of Reduction Type Tubular Titanium OxideParticles (RPT-3)

Reduction type tubular titanium oxide particles (RPT-3) were prepared inthe same manner as in Example B2, except that a plasma gas (NH₃: 3%, H₂:7%) was used as the gas in the reduction treatment.

The composition parameters of the resulting reduction type tubulartitanium oxide particles (RPT-3) and the amount of residual K₂O weremeasured. The results are set forth in Table 2. Further, a TEMphotograph of the particles was taken to determine an average particlelength (L), an average tube outer diameter (D_(out)) and an average tubeinner diameter (D_(in)). Furthermore, powder resistance was measured.The results are set forth in Table 2.

Example B4 Preparation of Titanium Oxide Particle (T-4) Dispersion

A peroxotitanic acid aqueous solution (TiO₂ concentration: 0.5% byweight) of 3800 g was prepared in the same manner as in Example B1. Theaqueous solution was mixed with 7.0 g of a silica sol (available fromCatalysts & Chemicals Industries Co., Ltd., SI-350, SiO₂ concentration:30% by weight, average particle diameter: 8 nm), and the mixture washeated at 95° C. for 3 hours to prepare a titanium oxide particle (T-4)dispersion having a TiO₂.SiO₂ concentration of 0.56% by weight. Anaverage particle diameter of the titanium oxide particles (T-4) is setforth in Table 2.

Preparation of Reduction Type Tubular Titanium Oxide Particles (RPT-4)

To the titanium oxide particle (T-3) dispersion, 70 g of a KOH aqueoussolution having a concentration of 40% by weight was added in such amanner that the molar ratio (A_(M))/(T_(M)) of the number of moles(A_(M)) of the alkali metal hydroxide to the number of moles (T_(M)) ofTiO₂ became 10, and the mixture was subjected to hydrothermal treatmentat 150° C. for 2 hours (first hydrothermal treatment).

The resulting particles were sufficiently washed with pure water. Theamount of residual K₂O was 1.5% by weight.

Then, a water dispersion (TiO₂.SiO₂ concentration: 3% by weight) of thetubular titanium oxide particles was prepared. To the water dispersion,a cation exchange resin and an anion exchange resin were added in thesame amount as that of the tubular titanium oxide particles, and themixture was treated at 60° C. for 24 hours (second hydrothermaltreatment). After sufficient washing with pure water again, a waterdispersion (TiO₂.SiO₂ concentration: 3% by weight) of the tubulartitanium oxide particles was prepared. To the water dispersion, citricacid was added in such an amount that the molar ratio of citric acid toTiO₂ became 0.1. The resulting dispersion had pH of 3. Then, thedispersion was subjected to hydrothermal treatment at 60° C. for 24hours (second hydrothermal treatment of the second time). Then, washingwith water and freeze drying were carried out to prepare tubulartitanium oxide particles (PT-4).

Subsequently, the tubular titanium oxide particles were subjected to thesame reduction treatment as in Example B1 to prepare reduction typetubular titanium oxide particles (RPT-4).

The composition parameters of the resulting reduction type tubulartitanium oxide particles (RPT-4) and the amount of residual K₂O weremeasured. The results are set forth in Table 2. Further, a TEMphotograph of the particles was taken to determine an average particlelength (L), an average tube outer diameter (D_(out)) and an average tubeinner diameter (D_(in)). Furthermore, powder resistance was measured.The results are set forth in Table 2.

Example B5 Preparation of Titanium Oxide Particle (T-5) Dispersion

A peroxotitanic acid aqueous solution (TiO₂ concentration: 0.5% byweight) of 3800 g was prepared in the same manner as in Example B1. Theaqueous solution was mixed with 15.8 g of a silica sol (available fromCatalysts & Chemicals Industries Co., Ltd., SI-550, SiO₂ concentration:30% by weight, average particle diameter: 8 nm), and the mixture washeated at 95° C. for 3 hours to prepare a titanium oxide particle (T-5)dispersion having a TiO₂.SiO₂ concentration of 0.62% by weight. Anaverage particle diameter of the titanium oxide particles (T-5) is setforth in Table 2.

Preparation of Reduction Type Tubular Titanium Oxide Particles (RPT-5)

To the titanium oxide particle (T-5) dispersion, 70 g of a KOH aqueoussolution having a concentration of 40% by weight was added in such amanner that the molar ratio (A_(M))/(T_(M)) of the number of moles(A_(M)) of the alkali metal hydroxide to the number of moles (T_(M)) ofTiO₂ became 10, and the mixture was subjected to hydrothermal treatmentat 150° C. for 2 hours (first hydrothermal treatment). The resultingparticles were sufficiently washed with pure water. The amount ofresidual K₂O was 2.0% by weight.

Then, a water dispersion (TiO₂.SiO₂ concentration: 3% by weight) of thetubular titanium oxide particles was prepared. To the water dispersion,a cation exchange resin and an anion exchange resin were added in thesame amount as that of the tubular titanium oxide particles, and themixture was treated at 60° C. for 24 hours (second hydrothermaltreatment). After sufficient washing with pure water again, a waterdispersion (TiO₂.SiO₂ concentration: 3% by weight) of the tubulartitanium oxide particles was prepared. To the water dispersion, citricacid was added in such an amount that the molar ratio of citric acid toTiO₂ became 0.1. The resulting dispersion had pH of 3. Then, thedispersion was subjected to hydrothermal treatment at 60° C. for 24hours (second hydrothermal treatment of the second time). Then, washingwith water and freeze drying were carried out to prepare tubulartitanium oxide particles (PT-5).

Subsequently, the tubular titanium oxide particles were subjected to thesame reduction treatment as in Example B1 to prepare reduction typetubular titanium oxide particles (RPT-5).

The composition parameters of the resulting reduction type tubulartitanium oxide particles (RPT-5) and the amount of residual K₂O weremeasured. The results are set forth in Table 2. Further, a TEMphotograph of the particles was taken to determine an average particlelength (L), an average tube outer diameter (D_(out)) and an average tubeinner diameter (D_(in)). Furthermore, powder resistance was measured.The results are set forth in Table 2.

Example B6 Preparation of Titanium Oxide Particle (T-6) Dispersion

A peroxotitanic acid aqueous solution (titanium oxide particle (T-1)dispersion, TiO₂ concentration: 0.5% by weight) of 3800 g was preparedin the same manner as in Example B1. The aqueous solution was mixed with19 g of a zirconia sol prepared in the following manner, and the mixturewas heated at 95° C. for 3 hours to prepare a titanium oxide particle(T-6) dispersion having a TiO₂.ZrO₂ concentration of 0.52% by weight. Anaverage particle diameter of the titanium oxide particles (T-6) is setforth in Table 2.

Preparation of Zirconia Sol

In a flask equipped with a dry distillation device, 5 kg of a zirconiumchloride aqueous solution containing 0.036% by weight of zirconiumchloride was placed, and with sufficient stirring, 290 g of 0.1 Nammonia water was slowly added. The resulting solution was heated at 95°C. for 50 hours to obtain an opaque white sol having a ZrO₂concentration of 0.034% by weight and pH of 1.8. Then, 0.1 N ammoniawater was further added to adjust pH to 4.8, and the resulting solutionwas washed with ion exchange water until no chlorine ion was detected inthe filtrate to prepare a zirconia sol (average particle diameter: 50nm) having a ZrO₂ concentration of 5% by weight as a dispersion.

Preparation of Reduction Type Tubular Titanium Oxide Particles (RPT-6)

To the titanium oxide particle (T-6) dispersion, 70 g of a KOH aqueoussolution having a concentration of 40% by weight was added in such amanner that the molar ratio (A_(M))/(T_(M)) of the number of moles(A_(M)) of the alkali metal hydroxide to the number of moles (T_(M)) ofTiO₂ became 10, and the mixture was subjected to hydrothermal treatmentat 150° C. for 2 hours (first hydrothermal treatment). The resultingparticles were sufficiently washed with pure water. The amount ofresidual K₂O was 1.7% by weight. Then, tubular titanium oxide particles(PT-6) were prepared in the same manner as in Example B5.

Subsequently, the tubular titanium oxide particles were subjected to thesame reduction treatment as in Example B1 to prepare reduction typetubular titanium oxide particles (RPT-6).

The composition parameters of the resulting reduction type tubulartitanium oxide particles (RPT-6) and the amount of residual K₂O weremeasured. The results are set forth in Table 2. Further, a TEMphotograph of the particles was taken to determine an average particlelength (L), an average tube outer diameter (D_(out)) and an average tubeinner diameter (D_(in)). Furthermore, electrical conductivity wasmeasured. The results are set forth in Table 2.

Comparative Example B1

As tubular titanium oxide particles, the tubular titanium oxideparticles (PT-1) prepared in Example B1 were used.

Comparative Example B2 Preparation of Tubular Titanium Oxide Particles(RPT-8)

Reduction type tubular titanium oxide particles (RPT-8) were prepared inthe same manner as in Example B1, except that the reduction treatmenttemperature was changed to 700° C.

The composition parameters of the resulting reduction type tubulartitanium oxide particles (RPT-8) and the amount of residual K₂O weremeasured. The results are set forth in Table 2. Further, a TEMphotograph of the particles was taken to determine an average particlelength (L), an average tube outer diameter (D_(out)) and an average tubeinner diameter (D_(in)). Furthermore, electrical conductivity wasmeasured. The results are set forth in Table 2.

Comparative Example B3 Preparation of Tubular Titanium Oxide Particles(RPT-9)

Reduction type tubular titanium oxide particles (RPT-9) were prepared inthe same manner as in Example B1, except that a H₂ gas was used insteadof the NH₃ gas and the reduction treatment temperature was changed to500° C.

The composition parameters of the resulting reduction type tubulartitanium oxide particles (RPT-9) and the amount of residual K₂O weremeasured. The results are set forth in Table 2. Further, a TEMphotograph of the particles was taken to determine an average particlelength (L), an average tube outer diameter (D_(out)) and an average tubeinner diameter (D_(in)). Furthermore, electrical conductivity wasmeasured. The results are set forth in Table 2.

Comparative Example B4

As tubular titanium oxide particles, the tubular titanium oxideparticles (PT-1) prepared in Example B4 were used to measure electricalconductivity. The result is set forth in Table 2.

TABLE 2 Titanium oxide type starting particles Average particleDispersion Reduction treatment diameter Concentration Temperature TimeComposition (nm) (wt. %) Atmosphere (° C.) (hr) Ex. B1 TiO₂ 100 30 0.5NH₃ 400 2 Ex. B2 TiO₂ 100 30 0.5 NH₃ 400 2 Ex. B3 TiO₂ 100 30 0.5 NH₃ +H₂ 300 2 Ex. B4 TiO₂•SiO₂ 90/10 20 0.56 NH₃ 400 2 Ex. B5 TiO₂•SiO₂ 80/2010 0.62 NH₃ 400 2 Ex. B6 TiO₂•SiO₂ 95/5  10 0.52 NH₃ 400 2 Comp. Ex. B1TiO₂ 100 30 0.5 — — — Comp. Ex. B2 TiO₂ 100 30 0.5 NH₃ 700 2 Comp. Ex.B3 TiO₂ 100 30 0.5 H₂ 550 2 Comp. Ex. B4 TiO₂•SiO₂ 90/10 20 0.56 — — —Tubular titanium oxide particles Average Average Average tube tubeparticle outer inner Composition (Ti_(a)M_(b)O_(x)N_(y)) Powder lengthdiameter diameter a b x y K₂O resistance (nm) (nm) (nm) (Ti) (M) (O) (N)(ppm) (Ω · cm) Ex. B1 180 10 7.5 1 — 1.2 0.02 250 5 Ex. B2 180 10 7.5 1— 1.2 0.02 50 0.5 Ex. B3 180 10 7.5 1 — 0.9 — 50 0.1 Ex. B4 145 10 7.50.9 0.1 1.22 0.02 40 100 Ex. B5 225 10 7.5 0.9 0.1 1.24 0.02 80 5000 Ex.B6 175 10 7.5 0.95  0.05 1.2 0.02 240 10 Comp. Ex. B1 180 10 7.5 1 — 20   250 5 × 10⁶ Comp. Ex. B2 180 10 7.5 1 — 0.98 0.04 250 0.05 Comp. Ex.B3 180 10 7.5 1 — 0.9 — 250 0.01 Comp. Ex. B4 145 10 7.5 0.9 0.1 2 0  40 1 × 10⁷

Preparation Example C1 Preparation of Titanium Oxide Particle (T-1)Dispersion

A titanium chloride aqueous solution was diluted with pure water toprepare a titanium chloride aqueous solution having a TiO₂ concentrationof 5% by weight. The aqueous solution was added to ammonia water havinga concentration of 15% by weight and having been controlled to atemperature of 5° C. to perform neutralization and hydrolysis. After theaddition of the titanium chloride aqueous solution, the resulting gelhad pH of 10.5. Then, the gel was washed by filtration to obtain a gelof orthotitanic acid having a TiO₂ concentration of 9% by weight.

Thereafter, 100 g of the gel of orthotitanic acid was dispersed in 2900g of pure water, then 800 g of hydrogen peroxide water having aconcentration of 35% by weight was added, and with stirring, the mixturewas heated at 85° C. for 3 hours to prepare a peroxotitanic acid aqueoussolution. The peroxotitanic acid aqueous solution obtained had a TiO₂concentration of 0.5% by weight.

Subsequently, the resulting solution was heated at 95° C. for 10 hoursto give a titanium oxide particle dispersion, and to the titanium oxideparticle dispersion, tetramethylammonium hydroxide (TMAH, MW: 149.2) wasadded in such an amount that the molar ratio of TMAH to TiO₂ in thedispersion became 0.016. The resulting dispersion had pH of 11. Then,the dispersion was subjected to hydrothermal treatment at 230° C. for 5hours to prepare a titanium oxide particle (T-1) dispersion. Thetitanium oxide particles (T-1) had an average particle diameter of 30nm.

Preparation of Tubular Titanium Oxide Particles (PT-1)

To the titanium oxide particle (T-1) dispersion, 70 g of a NaOH aqueoussolution having a concentration of 40% by weight was added in such amanner that the molar ratio (A_(M))/(T_(M)) of the number of moles(A_(M)) of the alkali metal hydroxide to the number of moles (T_(M)) ofTiO₂ became 10, and the mixture was subjected to hydrothermal treatmentat 150° C. for 10 hours.

The resulting particles were sufficiently washed with pure water. Then,alkali was decreased by the use of a cation exchange resin to preparetubular titanium oxide particles (PT-1-1). The amount of residual Na₂Owas 0.15% by weight.

Subsequently, to a water dispersion (TiO₂ concentration: 5% by weight)of the tubular titanium oxide particles (PT-1-1), tetramethylammoniumhydroxide (TMAH) was added as an organic base in such an amount that themolar ratio of TMAH to TiO₂ became 0.1. The resulting dispersion had pHof 13.2. Then, the dispersion was subjected to hydrothermal treatment at110° C. for 5 hours to prepare tubular titanium oxide particles (PT-1).

The resulting tubular titanium oxide particles (PT-1) were washed withwater and dried. Then, alkali was analyzed, and a TEM photograph of theparticles was taken to determine an average particle length (L), anaverage tube outer diameter (D_(out)) and an average tube inner diameter(D_(in)). Further, specific surface area of the particles and thecrystalline state thereof were evaluated. The results are set forth inTable 3.

Evaluation Criteria of Crystalline State

Evaluation was made based on the height of a peak at a lattice constantd of 1.89.

AA: The peak is obviously higher than that of the tubular titanium oxideparticles (PT-1-1).

BB: The peak is almost the same as that of the tubular titanium oxideparticles (PT-1-1).

CC: The peak is obviously lower than that of the tubular titanium oxideparticles (PT-1-1).

DD: The particles are substantially amorphous.

The crystal type (crystal form) of the particles (PT-1-1) was anatasetype.

Preparation Example C2 Preparation of Tubular Titanium Oxide Particles(PT-2)

Tubular titanium oxide particles (PT-2) were prepared in the same manneras in Preparation Example C1, except that instead of TMAH, citric acidwas added to the water dispersion (TiO₂ concentration: 5% by weight) ofthe tubular titanium oxide particles (PT-1-1) in such an amount that themolar ratio of citric acid to TiO₂ became 0.1.

The resulting tubular titanium oxide particles (PT-2) were washed withwater and dried. Then, alkali was analyzed, and a TEM photograph of theparticles was taken to determine an average particle length (L), anaverage tube outer diameter (D_(out)) and an average tube inner diameter(D_(in)). Further, specific surface area of the particles and thecrystalline state thereof were evaluated. The results are set forth inTable 3.

Preparation Example C3 Preparation of Tubular Titanium Oxide Particles(PT-3)

To a titanium oxide particle (T-1) dispersion prepared in the samemanner as described above, 40 g of a NaOH aqueous solution having aconcentration of 40% by weight and 358 g of a tetramethylammoniumhydroxide (TMAH) aqueous solution having a concentration of 25% byweight were added in such a manner that the molar ratio[(A_(M))+(OB_(M))]/(T_(M)) of the total of the number of moles (A_(M))of the alkali metal hydroxide and the number of moles (OB_(M)) of theorganic base to the number of moles (T_(M)) of TiO₂ became 10, and themixture was subjected to hydrothermal treatment at 150° C. for 2 hours.The resulting particles were sufficiently washed with pure water. Then,alkali was decreased by the use of a cation exchange resin to preparetubular titanium oxide particles (PT-2-1). The amount of residual Na₂Owas 0.12% by weight.

Subsequently, to a water dispersion (TiO₂ concentration: 5% by weight)of the tubular titanium oxide particles (PT-2-1), citric acid was addedin such an amount that the molar ratio of citric acid to TiO₂ became0.1. The resulting dispersion had pH of 3.0. Then, the dispersion wassubjected to hydrothermal treatment at 150° C. for 15 hours to preparetubular titanium oxide particles (PT-3).

The resulting tubular titanium oxide particles (PT-3) were washed withwater and dried. Then, alkali was analyzed, and a TEM photograph of theparticles was taken to determine an average particle length (L), anaverage tube outer diameter (D_(out)) and an average tube inner diameter(D_(in)). Further, specific surface area of the particles and thecrystalline state thereof were evaluated. The results are set forth inTable 3.

Preparation Example C4 Preparation of Titanium Oxide Particle (T-2)Dispersion

A peroxotitanic acid aqueous solution (TiO₂ concentration: 0.5% byweight) of 3800 g was prepared in the same manner as described above.The aqueous solution was mixed with 7.0 g of a silica sol (availablefrom Catalysts & Chemicals Industries Co., Ltd., SI-350, SiO₂concentration: 30% by weight, average particle diameter: 8 nm), and themixture was heated at 95° C. for 3 hours to prepare a titanium oxideparticle (T-2) dispersion having a TiO₂.SiO₂ concentration of 0.56% byweight. The titanium oxide particles (T-2) had an average particlediameter of 20 nm.

Preparation of Tubular Titanium Oxide Particles (PT-4)

To the titanium oxide particle (T-2) dispersion, 70 g of a NaOH aqueoussolution having a concentration of 40% by weight was added in such amanner that the molar ratio (A_(M))/(T_(M)) of the number of moles(A_(M)) of the alkali metal hydroxide to the number of moles (T_(M)) ofTiO₂ became 10, and the mixture was subjected to hydrothermal treatmentat 150° C. for 10 hours. The resulting particles were sufficientlywashed with pure water. Then, alkali was decreased by the use of acation exchange resin to prepare tubular titanium oxide particles(PT-4-1). The amount of residual Na₂O was 0.45% by weight.

Subsequently, to a water dispersion (TiO₂.SiO₂ concentration: 3% byweight) of the tubular titanium oxide particles (PT-4-1), citric acidwas added in such an amount that the molar ratio of citric acid to TiO₂became 0.1. The resulting dispersion had pH of 3.0. Then, the dispersionwas subjected to hydrothermal treatment at 150° C. for 15 hours toprepare tubular titanium oxide particles (PT-4).

The resulting tubular titanium oxide particles (PT-4) were washed withwater and dried. Then, alkali and SiO₂ were analyzed, and a TEMphotograph of the particles was taken to determine an average particlelength (L), an average tube outer diameter (D_(out)) and an average tubeinner diameter (D_(in)). Further, specific surface area of the particlesand the crystalline state thereof were evaluated. The results are setforth in Table 3.

Preparation Example C5 Preparation of Titanium Oxide Particle (T-3)Dispersion

A peroxotitanic acid aqueous solution (TiO₂ concentration: 0.5% byweight) of 3800 g was prepared in the same manner as described above.The aqueous solution was mixed with 15.8 g of a silica sol (availablefrom Catalysts & Chemicals Industries Co., Ltd., SI-550, SiO₂concentration: 30% by weight, average particle diameter: 8 nm), and themixture was heated at 95° C. for 3 hours to prepare a titanium oxideparticle (T-3) dispersion having a TiO₂.SiO₂ concentration of 0.62% byweight. The titanium oxide particles (T-3) had an average particlediameter of 10 nm.

Preparation of Tubular Titanium Oxide Particles (PT-5)

To the titanium oxide particle (T-3) dispersion, 7.0 g of a NaOH aqueoussolution having a concentration of 40% by weight was added in such amanner that the molar ratio (A_(M))/(T_(M)) of the number of moles(A_(M)) of the alkali metal hydroxide to the number of moles (T_(M)) ofTiO₂ became 10, and the mixture was subjected to hydrothermal treatmentat 150° C. for 2 hours. The resulting particles were sufficiently washedwith pure water. Then, alkali was decreased by the use of a cationexchange resin to prepare tubular titanium oxide particles (PT-5-1). Theamount of residual Na₂O was 0.50% by weight.

Subsequently, to a water dispersion (TiO₂.SiO₂ concentration: 3% byweight) of the tubular titanium oxide particles (PT-5-1), citric acidwas added in such an amount that the molar ratio of citric acid to TiO₂became 0.1. The resulting dispersion had pH of 3.0. Then, the dispersionwas subjected to hydrothermal treatment at 150° C. for 15 hours toprepare tubular titanium oxide particles (PT-5).

The resulting tubular titanium oxide particles (PT-5) were washed withwater and dried. Then, alkali and SiO₂ were analyzed, and a TEMphotograph of the particles was taken to determine an average particlelength (L), an average tube outer diameter (D_(out)) and an average tubeinner diameter (D_(in)). Further, specific surface area of the particlesand the crystalline state thereof were evaluated. The results are setforth in Table 3.

Preparation Example C6 Preparation of Titanium Oxide Particle (T-4)Dispersion

A peroxotitanic acid aqueous solution (TiO₂ concentration: 0.5% byweight) of 3800 g was prepared in the same manner as described above.The aqueous solution was mixed with 21 g of an alumina sol (availablefrom Catalysts & Chemicals Industries Co., Ltd., AS-2, Al₂O₃concentration: 10% by weight), and the mixture was heated at 95° C. for3 hours to prepare a titanium oxide particle (T-4) dispersion having aTiO₂.Al₂O₃ concentration of 0.55% by weight. The titanium oxideparticles (T-43) had an average particle diameter of 20 nm.

Preparation of Tubular Titanium Oxide Particles (PT-6)

To the titanium oxide particle (T-4) dispersion, 70 g of a NaOH aqueoussolution having a concentration of 40% by weight was added in such amanner that the molar ratio (A_(M))/(T_(M)) of the number of moles(A_(M)) of the alkali metal hydroxide to the number of moles (T_(M)) ofTiO₂ became 0.10, and the mixture was subjected to hydrothermaltreatment at 150° C. for 10 hours. The resulting particles weresufficiently washed with pure water. Then, alkali was decreased by theuse of a cation exchange resin to prepare tubular titanium oxideparticles (PT-6-1). The amount of residual Na₂O was 0.50% by weight.

Subsequently, to a water dispersion (TiO₂.Al₂O₃ concentration: 3% byweight) of the tubular titanium oxide particles (PT-6-1), citric acidwas added in such an amount that the molar ratio of citric acid to TiO₂became 0.1. The resulting dispersion had pH of 3.0. Then, the dispersionwas subjected to hydrothermal treatment at 150° C. for 15 hours toprepare tubular titanium oxide particles (PT-6).

The resulting tubular titanium oxide particles (PT-6) were washed withwater and dried. Then, alkali and Al₂O₃ were analyzed, and a TEMphotograph of the particles was taken to determine an average particlelength (L), an average tube outer diameter (D_(out)) and an average tubeinner diameter (D_(in)). Further, specific surface area of the particlesand the crystalline state thereof were evaluated. The results are setforth in Table 3.

Preparation Example C7 Preparation of Titanium Oxide Particle. (T-5)Dispersion

A peroxotitanic acid aqueous solution (TiO₂ concentration: 0.5% byweight) of 3800 g was prepared in the same manner as described above.The aqueous solution was mixed with 19 g of a zirconia sol prepared inthe following manner, and the mixture was heated at 95° C. for 3 hoursto prepare a titanium oxide particle (T-5) dispersion having a TiO₂.ZrO₂concentration of 0.52% by weight. The titanium oxide particles (T-5) hadan average particle diameter of 10 nm.

Preparation of Zirconia Sol

In a flask equipped with a dry distillation device, 5 kg of a zirconiumchloride aqueous solution containing 0.036% by weight of zirconiumchloride was placed, and with sufficient stirring, 290 g of 0.1 Nammonia water was slowly added. The resulting solution was heated at 95°C. for 50 hours to obtain an opaque white sol having a ZrO₂concentration of 0.034% by weight and pH of 1.8. Then, 0.1 N ammoniawater was further added to adjust pH to 4.8, and the resulting solutionwas washed with ion exchange water until no chlorine ion was detected inthe filtrate to prepare a zirconia sol (average particle diameter: 50nm) having a ZrO₂ concentration of 5% by weight as a dispersion.

Preparation of Tubular Titanium Oxide Particles (PT-7)

To the titanium oxide particle (T-5) dispersion, 70 g of a NaOH aqueoussolution having a concentration of 40% by weight was added in such amanner that the molar ratio (A_(M))/(T_(M)) of the number of moles(A_(M)) of the alkali metal hydroxide to the number of moles (T_(M)) ofTiO₂ became 10, and the mixture was subjected to hydrothermal treatmentat 150° C. for 10 hours. The resulting particles were sufficientlywashed with pure water. Then, alkali was decreased by the use of acation exchange resin to prepare tubular titanium oxide particles(PT-7-1). The amount of residual Na₂O was 0.3% by weight.

Subsequently, to a water dispersion (TiO₂.ZrO₂ concentration: 3% byweight) of the tubular titanium oxide particles (PT-7-1), citric acidwas added in such an amount that the molar ratio of citric acid to TiO₂became 0.1. The resulting dispersion had pH of 3.0. Then, the dispersionwas subjected to hydrothermal treatment at 150° C. for 15 hours toprepare tubular titanium oxide particles (PT-7).

The resulting tubular titanium oxide particles (PT-7) were washed withwater and dried. Then, alkali and ZrO₂ were analyzed, and a TEMphotograph of the particles was taken to determine an average particlelength (L), an average tube outer diameter (D_(out)) and an average tubeinner diameter (D_(in)). Further, specific surface area of the particlesand the crystalline state thereof were evaluated. The results are setforth in Table 3.

Comparative Preparation Example C1 Preparation of Titanium OxideParticle (T-6) Dispersion

A titanium oxide particle (T-1) dispersion prepared in the same manneras described above was dried and then calcined at 600° C. for 2 hours.The calcined product was pulverized to obtain a titanium oxide powderhaving an average particle diameter of 200 nm. Then, the powder wasdispersed in water to prepare a titanium oxide particle (T-6) dispersionhaving a TiO₂ concentration of 10% by weight.

Preparation of Tubular Titanium Oxide Particles (PT-8)

To the titanium oxide particle (T-6) dispersion, 70 g of a NaOH aqueoussolution having a concentration of 40% by weight was added in such amanner that the molar ratio (A_(M))/(T_(M)) of the number of moles(A_(M)) of the alkali metal hydroxide to the number of moles (T_(M)) ofTiO₂ became 10, and the mixture was subjected to hydrothermal treatmentat 150° C. for 2 hours. The resulting particles were sufficiently washedwith pure water. Then, alkali was decreased by the use of a cationexchange resin to prepare tubular titanium oxide particles (PT-8-1). Theamount of residual Na₂O was 0.60% by weight.

Subsequently, to a water dispersion (TiO₂ concentration: 3% by weight)of the tubular titanium oxide particles (PT-8-1), tetramethylammoniumhydroxide (TMAH) was added as an organic base in such an amount that themolar ratio of TMAH to TiO₂ became 0.1. The resulting dispersion had pHof 13.2. Then, the dispersion was subjected to hydrothermal treatment at110° C. for 5 hours to prepare tubular titanium oxide particles (PT-8).

The resulting tubular titanium oxide particles (PT-8) were washed withwater and dried. Then, alkali was analyzed, and a TEM photograph of theparticles was taken to determine an average particle length (L), anaverage tube outer diameter (D_(out)) and an average tube inner diameter(D_(in)). Further, specific surface area of the particles and thecrystalline state thereof were evaluated. The results are set forth inTable 3.

Comparative Preparation Example C2 Preparation of Titanium OxideParticle (T-7) Dispersion

A titanium oxide particle (T-3) dispersion prepared in the same manneras described above was dried and then calcined at 600° C. for 2 hours.The calcined product was pulverized to obtain a titanium oxide powderhaving an average particle diameter of 300 nm. Then, the powder wasdispersed in water to prepare a titanium oxide particle (T-7) dispersionhaving a TiO₂.SiO₂ concentration of 10% by weight.

Preparation of Tubular Titanium Oxide Particles (PT-9)

To the titanium oxide particle (T-7) dispersion, 70 g of a NaOH aqueoussolution having a concentration of 40% by weight was added in such amanner that the molar ratio (A_(M))/(T_(M)) of the number of moles(A_(M)) of the alkali metal hydroxide to the number of moles (T_(M)) ofTiO₂ became 10, and the mixture was subjected to hydrothermal treatmentat 150° C. for 1 hours. The resulting particles were sufficiently washedwith pure water. Then, alkali was decreased by the use of a cationexchange resin to prepare tubular titanium oxide particles (PT-9-1). Theamount of residual Na₂O was 0.70% by weight.

Subsequently, to a water dispersion (TiO₂ concentration: 3% by weight)of the tubular titanium oxide particles (PT-9-1), tetramethylammoniumhydroxide (TMAH) was added as an organic base in such an amount that themolar ratio of TMAH to TiO₂ became 0.1. The resulting dispersion had pHof 13.2. Then, the dispersion was subjected to hydrothermal treatment at150° C. for 15 hours to prepare tubular titanium oxide particles (PT-9).

The resulting tubular titanium oxide particles (PT-9) were washed withwater and dried. Then, alkali and SiO₂ were analyzed, and a TEMphotograph of the particles was taken to determine an average particlelength (L), an average tube outer diameter (D_(out)) and an average tubeinner diameter (D_(in)). Further, specific surface area of the particlesand the crystalline state thereof were evaluated. The results are setforth in Table 3.

Comparative Preparation Example C3 Preparation of Tubular Titanium OxideParticles (PT-10)

Tubular titanium oxide particles (PT-10) were prepared in the samemanner as in Comparative Preparation Example C2, except that instead ofTMAH, citric acid was added to the water dispersion (TiO₂ concentration:5% by weight) of the tubular titanium oxide particles (PT-9-1) in suchan amount that the molar ratio of citric acid to TiO₂ became 0.1.

The resulting tubular titanium oxide particles (PT-10) were washed withwater and dried. Then, alkali was analyzed, and a TEM photograph of theparticles was taken to determine an average particle length (L), anaverage tube outer diameter (D_(out)) and an average tube inner diameter(D_(in)). Further, specific surface area of the particles and thecrystalline state thereof were evaluated. The results are set forth inTable 3.

Example C1 Metal Oxide Semiconductor Film (A)

In 2 liters of pure water, 10 g of a titanium hydride powder wassuspended, and to the resulting suspension, 800 g of hydrogen peroxidewater having a concentration of 5% by weight was added over a period of30 minutes. Then, the mixture was heated to 80° C. to prepare a solutionof peroxotitanic acid.

A dispersion (oxide concentration: 10%) of the tubular titanium oxideparticles (PT-1) was prepared, and the dispersion was mixed with theabove-prepared peroxotitanic acid solution in such a manner that theweight ratio (peroxotitanic acid/tubular titanium oxide particles(PT-1), in terms of an oxide) of the peroxotitanic acid to the tubulartitanium oxide particles (PT-1) became 0.1. Then, to the mixture,hydroxypropyl cellulose was added as a film forming aid in such anamount that the amount of all the oxides in the mixture became 30% byweight, to prepare a coating solution for forming a semiconductor film.

Subsequently, the coating solution was applied onto a transparent glassplate on which an electrode layer of fluorine-doped tin oxide had beenformed, and the coating layer was air dried and then irradiated withultraviolet rays of 6000 mJ/cm² by the use of a low-pressure mercurylamp to decompose peroxotitanic acid and thereby cure the coating film.The resulting film was heated at 300° C. for 30 minutes to performdecomposition of hydroxypropyl cellulose and annealing. Thus, a metaloxide semiconductor film (A) having a film thickness of 15 μm wasformed.

A pore volume and an average pore diameter of the metal oxidesemiconductor film (A) obtained were determined by a nitrogen adsorptionmethod. The results are set forth in Table 3.

Adsorption of Photosensitizer

Subsequently, an ethanol solution (concentration: 3×10⁻⁴ mol/liter) of aruthenium complex represented bycis-(SCN⁻)-bis(2,2′-bipyridyl-4,4′-dicarboxylate)ruthenium(II) as aphotosensitizer was prepared. The photosensitizer solution was appliedonto the metal oxide semiconductor film (A) by the use of a spinner andthen dried. The application and drying process was carried out fivetimes. An adsorption amount of the photosensitizer on the metal oxidesemiconductor film is set forth in Table 3.

Preparation of Photovoltaic Cell

In a mixed solvent of acetonitrile and ethylene carbonate in a volumeratio of 1:4 (acetonitrile:ethylene carbonate), tetrapropylammoniumiodide and iodine were dissolved in such amounts that thetetrapropylammonium iodide concentration became 0.46 mol/liter and theiodine concentration became 0.06 mol/liter, to prepare an electrolyticsolution.

The electrode previously prepared was used as one electrode, and as theother electrode, fluorine-doped tin oxide was used. On this electrode, atransparent glass substrate on which platinum had been supported wasarranged in such a manner that the electrodes faced each other, and thesides were sealed with a resin. Then, the electrolytic solution wasenclosed between the electrodes, and the electrodes were connected toeach other with a lead wire to prepare a photovoltaic cell (A).

The photovoltaic cell (A) was irradiated with light having an intensityof 100 W/m² by the use of a solar simulator to measure Voc (voltage in astate of open circuit), Joc (current density in case of short circuit),FF (curve factor) and η (conversion efficiency). The results are setforth in Table 3.

Preparation of Photocatalyst

A photocatalyst (AC) was prepared in the same manner as in thepreparation of the metal oxide semiconductor film (A), except that atransparent glass substrate on which no electrode layer was formed wasused and the coating film was heated at 450° C. for 30 minutes aftercured.

Activity Evaluation

A quartz cell (for optical measurements, 10×10×45 mm) was filled with amethylene blue solution having a concentration of 10 ppm. Then, thephotocatalyst (AC) was immersed in the solution and irradiated with a Xelamp (2 KW, spectral wavelength region: 209 to 706 nm). After 5 hours,an absorbance at a wavelength of 460 nm was measured. The absorbance ofthe solution measured before irradiation with the lamp was taken as 1. Alower absorbance indicates that the reaction proceeds more rapidly andmethylene blue is decreased. The result is set forth in Table 3.

Examples C2 to C7, Comparative Examples C1 to C3 Preparation ofPhotovoltaic Cells (B) to (H)

Photovoltaic cells (B) to (H) were prepared in the same manner as inExample C1, except that the tubular titanium oxide particles (PT-2) to(PT-10) were each used. Then, Voc, Joc, FF and η were measured. Theresults are set forth in Table 3.

Preparation of Photocatalysts (BC) to (HC)

Photovoltaic cells (BC) to (HC) were prepared in the same manner as inExample C1, except that the tubular titanium oxide particles (PT-2) to(PT-10) were each used. Then, the activity was evaluated. The resultsare set forth in Table 3.

TABLE 3 Tubular titanium oxide particles Photovaltaic cell semiconductorfilm Average Average Average Specific Average Adsorption Photovoltaiccell Photo- particle tube outer tube inner surface Pore pore amount ofJoc catalytic length diameter diameter Crystalline area volume diameterphotosensitizer Voc (mA/ η activity (nm) (nm) (nm) state (m²/g) (ml/g)(nm) (μg/cm²) (V) cm²) FF (%) Absorbance Ex. C1 180 10 7.5 anatase 4500.6 7.5 70 0.70 15 0.75 7.9 0.30 AA Ex. C2 180 10 7.5 anatase 450 0.67.5 70 0.70 15 0.75 7.9 0.25 AA Ex. C3 175 10 7.5 anatase 400 0.6 7.5 700.75 16 0.80 9.6 0.25 AA Ex. C4 145 10 7.5 anatase 500 0.6 7.5 60 0.75 50.50 1.9 0.10 AA Ex. C5 225 10 7.5 anatase 450 0.6 7.5 55 0.75 3 0.400.9 0.05 AA Ex. C6 175 10 7.5 anatase 450 0.6 7.5 55 0.75 9 0.60 4.10.25 AA Ex. C7 175 10 7.5 anatase 500 0.6 7.5 55 0.75 10 0.60 4.5 0.20AA Comp. 375 10 *1 7.5 anatase + Am 450 0.6 7.5 50 0.70 11 0.65 5.0 0.45Ex. C1 CC Comp. 375 10 *1 7.5 anatase + Am 500 0.6 7.5 50 0.70 2 0.200.3 0.40 Ex. C2 CC Comp. 375 10 *1 7.5 anatase + Am 500 0.6 7.5 50 0.702 0.20 0.3 0.38 Ex. C3 CC Notes: Am: amorphous *1 A part of theparticles are agglomerated.

1. A process for preparing tubular crystalline titanium oxide-containingparticles, comprising: (a) preparing titanium oxide particles fromperoxotitanic acid; and (b) subjecting a water dispersion sol, which isobtained by dispersing (i) the titanium oxide particles and/or (ii)titanium oxide type composite oxide particles comprising the titaniumoxide particles and oxide particles other than titanium oxide in water,said particles having an average particle diameter of 2 to 100 nm, tohydrothermal treatment in the presence of an alkali metal hydroxide toform tubular crystalline titanium oxide-containing particles.
 2. Theprocess for preparing tubular crystalline titanium oxide-containingparticles as claimed in claim 1, wherein reduction treatment is carriedout after the hydrothermal treatment.
 3. The process for preparingtubular crystalline titanium oxide-containing particles as claimed inclaim 2, wherein the reduction treatment comprises nitriding treatment.4. The process for preparing tubular crystalline titaniumoxide-containing particles as claimed in claim 1, wherein thehydrothermal treatment is carried out in the presence of aramoniumhydroxide and/or an organic base together with the alkali metalhydroxide.
 5. The process for preparing tubular crystalline titaniumoxide-containing particles as claimed in claim 1, wherein the oxideother than titanium oxide is an oxide of one or more elements selectedfrom Group Ia, Group Ib, Group IIa, Group IIb, Group IIIa, Group IIIb,Group IVa, Group IVb, Group Va, Group Vb, Group VIa, Group VIb, GroupVIIa and Group VIII of the periodic table.
 6. The process for preparingtubular crystalline titanium oxide-containing particles as claimed inclaim 5, wherein the oxide other than titanium oxide is one or moreoxides selected from SiO₂, ZrO₂, ZnO, Al₂O₃, CeO₂, Y₂O₃, Nd₂O₃, WO₃,Fe₂O₃ and Sb₂O₅.
 7. Tubular crystalline titanium oxide-containingparticles obtained by the process of claim 6 and having a sodium contentof not more than 0.1% by weight in terms of Na₂O.
 8. Tubular crystallinetitanium oxide-containing particles obtained by the process of claim 5and having a sodium content of not more than 0.1% by weight in terms ofNa₂O.
 9. Tubular crystalline titanium oxide-containing particlesobtained by the process of claim 1 and having a sodium content of notmore than 0.1% by weight in terms of Na₂O.
 10. Tubular crystallinetitanium oxide-containing particles obtained by the process of claim 1and having a sodium content of not more than 0.1% by weight in terms ofNa₂O.
 11. A process for preparing tubular crystalline titaniumoxide-containing particles, comprising: (a) preparing titanium oxideparticles from peroxotitanic acid; and (b) subjecting a water dispersionof the titanium oxide particles and/or titanium oxide type compositeoxide particles comprising the titanium oxide particles and oxideparticles other than titanium oxide, said titanium oxide particlesand/or composite oxide particles having an average particle diameter of2 to 100 nm, to hydrothermal treatment in the presence of an alkalimetal hydroxide, and then subjecting the water dispersion to reductiontreatment to form tubular crystalline titanium oxide-containingparticles.
 12. The process for preparing tubular crystalline titaniumoxide-containing particles as claimed in claim 11, wherein the reductiontreatment comprises nitriding treatment.
 13. The process for preparingtubular crystalline titanium oxide-containing particles as claimed inclaim 11, wherein ammonium hydroxide and/or one or more organic basesare allowed to be present together with the alkali metal hydroxide. 14.The process for preparing tubular crystalline titanium oxide-containingparticles as claimed in claim 11, wherein the oxide other than titaniumoxide is an oxide of one or more elements selected from Group Ia, GroupIb, Group IIa, Group IIb, Group IIIa, Group IIIb, Group IVa, Group IVb,Group Va, Group Vb, Group VIa, Group VIb, Group VIIa and Group VIII ofthe periodic table.
 15. Tubular crystalline titanium oxide-containingparticles obtained by the process of claim 11 and having a sodiumcontent of not more than 0.1% by weight in terms of Na₂O.
 16. Tubularcrystalline titanium oxide-containing particles represented by thefollowing compositional formula (1):Ti_(a)M_(b)O_(x)N_(y)  (1) wherein a and b are numbers satisfying theconditions of a+b=1 and b=0˜0.2, x and y are numbers satisfying theconditions of 1≦x+y<2, 1≦x<2 and 0≦y<0.2, and M is an element other thanTi, and containing crystalline titanium oxide as a main component,wherein the crystalline titanium oxide is obtained by a process ofpreparing titanium oxide particles from peroxotitanic acid.
 17. Thetubular crystalline titanium oxide-containing particles as claimed inclaim 16, having an outer diameter (D_(out)) of 5 to 40 nm, an innerdiameter (D_(in)) of 4 to 20 nm, a tube thickness of 0.5 to 10 nm, alength (L) of 50 to 1000 nm and a length (L)/outer diameter (D_(out))ratio (L/D_(out)) of 10 to
 200. 18. The tubular crystalline titaniumoxide-containing particles as claimed in claim 17, wherein the element Mother than titanium is one or more elements selected from Group Ia,Group Ib, Group IIa, Group IIb, group IIIa, Group IIIb, Group IVa, GroupIVb, Group Va, Group Vb, Group VIa, Group VIb, Group VIIa and Group VIIIof the periodic table.
 19. The tubular crystalline titaniumoxide-containing particles as claimed in claim 16, wherein the element Mother than titanium is one or more elements selected from Group Ia,Group Ib, Group IIa, Group IIb, Group IIIa, Group IIIb, Group IVa, GroupIVb, Group Va, Group Vb, Group VIa, Group VIb, Group VIIa and Group VIIIof the periodic table.
 20. The tubular crystalline titaniumoxide-containing particles as claimed in claim 19, wherein the element Mother than titanium is one or more elements selected from Si, Zr, Zn,Al, Ce, Y, Nd, W, Fe and Sb.